IB Physics Core Notes

Topic 2 Mechanics 2.1 Kinematics 2.1.1 Define displacement, velocity, speed and acceleration. Displacement-

Defined as the change in position of an object. Displacement is a quantity that has both direction and magnitude, it is a vector. Measured in metres.

Speed-

How far an object travels in a given time. Rate of change of distance (ms-1)

Velocity-

The vector version of speed. Tells us the magnitude of how fast an object is moving and the direction in which it is moving. (ms-1)

AverageVelocity = Acceleration-

Displacement TimeElapsed

Rate of change of velocity (ms-2)

AverageAcceleration =

ChangeInVelocity TimeElapsed

2.1.2 Explain the difference between instantaneous and average values of speed, velocity and acceleration. Instantaneous values of velocity speed and acceleration are taken at a particular moment. In any realistic situation they will be constantly varying and is not always meaningful or useful to know this e.g. drivers need to keep their instantaneous speed below the speed limit. Average velocity, speed and acceleration are taken over a certain period of time or distance. E.g. Average speed between Porto and Lisbon = distance/time = 350/km/3 hours 30 min = 100 kmh-1

2.1.3 Outline the conditions under which the equations for uniformly accelerated motion may be applied. The following equations of motion may be applied to an object that has a constant acceleration.

a=

(v − u ) t

s = ut + 12 at 2 v 2 = u 2 + 2as v= final velocity/ ms-1) u= initial velocity / ms-1 a= acceleration/ ms-2 s= displacement/m t=time/s

2.1.4 Identify the acceleration of a body falling in a vacuum near the Earth’s surface with the acceleration g of free fall.

Free fall is the uniform acceleration (ignoring the effect of air resistance) in the vertical direction of an object in a uniform gravitational field. All falling objects have the same acceleration independent of their masses. On earth all objects accelerate towards the ground at 9.81 ms-2.

Acceleration due to gravity can be measured in a number of ways. In the arrangement that is shown a timer starts when the ball is released form an electromagnet and stops when the ball passes through a gate at the bottom. The acceleration due to gravity can then be calculated using:

g=

2s t2

Acceleration due to gravity can also be calculated using light gates of ticker timers.

2.1.5 Solve problems involving the equations of uniformly accelerated motion. This question is about throwing a stone from a cliff. Antonia stands at the edge of a vertical cliff and throws a stone vertically upwards. v = 8.0ms –1

Sea

–1 The stone leaves Antonia’s hand with a speed v = 8.0ms . –2 The acceleration of free fall g is 10 m s and all distance measurements are taken from the point where the stone leaves Antonia’s hand. (a)

Ignoring air resistance calculate (i)

the maximum height reached by the stone.

v 2 = u 2 + 2as v2 s= 2s

s=

82 2 × 10

s = 3 .2 m (2) (ii)

the time taken by the stone to reach its maximum height.

a=

v−u t

t=

v−u a

t=

8 10

t = 0 .8 s (1) The time between the stone leaving Antonia’s hand and hitting the sea is 3.0 s. (b)

Determine the height of the cliff. Time to go form top of cliff to sea = 3.0 – (2 x 0.8) = 1.4s

s = ut + 12 at 2 s = (8.0 × 1.4) + ( 12 × 10 × 1.4 2 ) s = 21m

(3) (Total 6 marks)

2.1.6 Describe the effects of air resistance on falling objects. Air resistance acts upon all moving objects. As the velocity of an object increases the size of the air resistance also increases. Eventually the force of air resistance will equal the force of gravity. When this happens the object will stop accelerating. It has reached its terminal velocity.

The terminal velocity of an object is dependant on its shape. A feather has a lower terminal velocity than a hammer.

2.1.7 Draw and analyse distance–time graphs, displacement–time graphs, velocity–time graphs and acceleration–time graphs. Displacement – time graphs The object then is stationary for three seconds.

12 Object travels at a

dispalcement / m

10constant speed for the first five seconds

8

The object returns to its original location at a faster speed.

6 4 2 0 0

2

4

6 time /s

The gradient of a displacement - time graph is the velocity.

8

10

12

Velocity – time graphs

10 9

velocity / m/s

8 7 6 The object is slowing down.

5 4 objects The velocity is 3 increasing 2 1 0 0

5

10

15

time /s

The gradient of a velocity – time graph tells the acceleration of the object. If the line is flat the object is travelling at a constant velocity. The area under the graph represents the distance travelled. Acceleration – time graphs The area under an acceleration – time graph represents the change in velocity.

2.1.8 Calculate and interpret the gradients of displacement–time graphs and velocity–time graphs, and the areas under velocity–time graphs and acceleration–time graphs. 1) The graph shows the variation with time t of the velocity v of an object. v

t

Which one of the following graphs best represents the variation with time t of the acceleration a of the object?

A.

a

0

C.

B.

0

0

0

t

a

D.

0

t

a

0

t

0

t

a

0

2) An athlete runs round a circular track at constant speed. Which one of the following graphs best represents the variation with time t of the magnitude d of the displacement of the athlete from the starting position during one lap of the track? A. d

0

B. d

0

t

C. d

0

0

0

t

0

t

D. d

0

t

0

2.1.9 Determine relative velocity in one and in two dimensions. Frames of Reference: If two things are moving in the same straight line but are travelling at different speeds, then we can work out their relative velocities by simple addition or subtraction as appropriate. For example, imagine two cars travelling along a straight road at different speeds. If one car (travelling at 30 m/s) overtakes the other car (travelling at 25 m/s), then according to the driver of the slow car, the relative velocity of the fast car is 5 m/s. In technical terms what we are doing is moving from one frame of reference into another. The velocities of 25 m/s and 30 m/s were measured according to a stationary observer on the side of the road. We moved from this frame of reference into the driver’s frame of reference.

2.2 Force and Dynamics 2.2.1 Calculate the weight of a body using the expression W = mg. The term weight can mean different things to Physics. Some define it as the gravitational force acting on a mass, other define it as the reading on a supporting scale. Weight is a force and as the strength of gravity varies depending on where you are the weight of an object will also vary.

Weight = mass × Gravitatio nalFieldSt rength The mass of an object is a single quantity but has tow different properties – Gravitational Mass and Inertial Mass. The inertial mass of an object determines how that object will respond to a given force. The gravitational mass of an object tells us how much gravitational force that an object will feel when it is near another object. Although the two quantities are different they turn out to be equivalent. The fact that all objects accelerate at the same rate shows this.

2.2.2 Identify the forces acting on an object and draw free-body diagrams representing the forces acting. Free body diagrams show the size and direction all of the forces acting on an object. A simple situation is a bag resting on a table.

Free body diagram for the shopping Gravity is pulling the bag downwards and the reaction from the table is pushing the bag up.

Free body diagram for the table

2.2.3 Determine the resultant force in different situations. It is unusual for only one force to be acting on an object. Usually we have to add the forces together to calculate the resultant force.

If the forces are acting in one dimension then they can be simply added together as shown below.

If the forces are not in the same dimension then the resultant force can be drawn onto a scale diagram. Force F1 has been moves so that it is “nose to tail” with F2. The resultant force can then be drawn onto the diagram showing its magnitude and direction.

2.2.4 State Newton’s first law of motion. “Every body perseveres in its state of being at rest or of moving uniformly straight forward, except insofar as it is compelled to change its state by force impressed.” "A particle will stay at rest or continue at a constant velocity unless acted upon by an external unbalanced net force."

2.2.5 Describe examples of Newton’s first law. When a car moves at a steady speed all forces acting on it are balanced.

2.2.6 State the condition for translational equilibrium. “The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed.”

2.2.7 Solve problems involving translational equilibrium.

2.2.8 State Newton’s second law of motion.

2.2.9 Solve problems involving Newton’s second law. 2.2.10 Define linear momentum and impulse. Linear momentum is defined as the product of mass and velocity. P=mv where p= linear momentum/ kgms-1 m= mass/Kg v= velocity/ ms-1 Impulse is the product of Force and time I= Ft I= impulse/Ns F= Force/N t=time/s It can be shown that linear momentum and impulse have the same units. Ns = Kgms-2s Ns = Kgms-1 So impulse and momentum are the same quantity. In other words: Impulse = change in linear momentum. This is very useful for calculations. Force/time graphs – The area under a force-time graph is the impulse.

2.2.11 Determine the impulse due to a time-varying force by interpreting a force–time graph. 2.2.12 State the law of conservation of linear momentum. “In a closed system the fatal linear momentum is constant” e.g. Total momentum before a collision = Total momentum after a collision or Total momentum after an explosion = 0

2.2.13 Solve problems involving momentum and impulse. 2.2.14 State Newton’s third law of motion. For a force there is always an equal and opposite reaction: or the forces of two bodies on each other are always equal and are directed in opposite directions. When two bodies A and B interact, the force that A exerts on B is equal and opposite to the force that exerts on A.

2.2.15 Discuss examples of Newton’s third law.

If one roller-skater pushes another, they both feel a force. The forces must be equal and opposite, but the acceleration will be different. A book exerting a force of 10N in a table the table will also exert 10N back.

2.3 Work, energy and power 2.3.1 Outline what is meant by work. Work is what is accomplished when a force acts on an object as the object moves through a distance. Work Done = Force x Distance W=Fs Work is a form of energy and is measured in joules.

2.3.2 Determine the work done by a non-constant force by interpreting a force–displacement graph. As work is the product of force and distance, it can be represented as the area under a graph of force as a function of distance. In the below graph the shaded region represents the work done on an object that undergoes a constant force. Thus, the work done (area of the shaded region) can be calculated by multiplying distance (base) by force (height).

This graphical method of calculating work is also useful in estimating the work that results from a varying force. The force applied to the object in changes over time.

The work done cannot be calculated by finding the area of a simple rectangle but it can be estimated by dividing the area into small segments, calculating the area of each segment, and adding all of the segment areas.

Such areas are often divided into rectangles because the area of a rectangle is easily calculated. However, triangles, trapezoids, or any type of segments may be used. The better the segments fit the area, the more precise the estimate.

2.3.3 Solve problems involving the work done by a force. The diagram below shows the variation with displacement x of the force F acting on an object in the direction of the displacement.

F R Q

S

P

0 W 0

V x1

T x2

x

Which area represents the work done by the force when the displacement changes from x1 to x2? A.

QRS

B.

WPRT

C.

WPQV

D.

VQRT

2.3.4 Outline what is meant by kinetic energy. Kinetic Energy: The energy of a moving body because of its movement.

K.E. = ½ mv2

The unit of Kinetic Energy is the joules /J.

2.3.5 Outline what is meant by change in gravitational potential energy. Gravitational potential energy is energy that is stored in an object by its height.

∆G.P.E = mg∆h

The unit of gravitational potential energy is the joule /J.

2.3.6 State the principle of conservation of energy. Energy is conserved; this means that the total amount of energy in the universe is constant. Energy cannot be made or destroyed.

It can be transformed from one form to another.

2.3.7 List different forms of energy and describe examples of the transformation of energy from one form to another. Kinetic Energy Gravitational Potential Elastic Potential Energy

Electrostatic Potential Thermal Energy Electrical Energy

Chemical energy Nuclear energy Internal Energy

Radiant energy Solar energy Light energy

Situation

Energy Conversion

Formula

Brakes get hot

K.E. -» Thermal Energy

½ mv2 = mc∆T

Car going up hill

K.E. -» GPE

½mv2 = mgh

Stone falling

GPE –» K.E.

mgh = ½mv2

2.3.8 Distinguish between elastic and inelastic collisions. Most collisions are inelastic because kinetic energy is transferred to other forms of energy— such as thermal energy, potential energy, and sound—during the collision process. If you are asked to determine if a collision is elastic or inelastic, calculate the kinetic energy of the bodies before and after the collision. If kinetic energy is not conserved, then the collision is inelastic. Momentum is conserved in all inelastic collisions.

An elastic collision is a collision where no mechanical energy is lost. The collision of pool balls is a good example of an elastic collision. Although some energy is lost (as sound energy) this is a small fraction of the total energy.

For elastic collisions the relative velocity before is always equal to the relative velocity after the collision. Particles in an ideal gas collide elastically.

2.3.9 Define power. Power is the rate of doing work or transferring energy.

Power =

WorkDone time

The unit of power is the Watt (W). 1 watt is equivalent to 1 Joule of energy being transformed per second.

2.3.10 Define and apply the concept of efficiency. In any energy transfer some of the work is transferred into a form that is not useful. This energy is wasted. Efficiency is defined as the ratio of the useful energy to the total energy transferred.

Efficiency =

UsefulEnergyOut TotalEnerg yIn

Efficiency does not have any units and is usually expressed as a percentage.

2.3.11 Solve problems involving momentum, work, energy and power.

1) This question is about projectile motion and the use of an energy argument to find the speed with which a thrown stone lands in the sea. Christina stands close to the edge of a vertical cliff and throws a stone. The diagram below (not drawn to scale) shows part of the trajectory of the stone. Air resistance is negligible.

Point P on the diagram is the highest point reached by the stone and point Q is at the same height above sea level as point O. (a)

At point P on the diagram above draw arrows to represent (i)

the acceleration of the stone (label this A). (1)

(ii)

the velocity of the stone (label this V). (1)

−1 The stone leaves Christina’s hand (point O) at a speed of 15 m s in the direction shown. Her hand is at a height of 25 m above sea level. The mass of the −2 stone is 160 g. The acceleration due to gravity g = 10 m s . (b)

(i)

Calculate the kinetic energy of the stone immediately after it leaves Christina’s hand. KE

=

1 2

mv

2

= 0.08 × 225 = 18 J

(1) (ii)

State the value of the kinetic energy at point Q. 18 J

(1)

(iii)

Calculate the loss in potential energy of the stone in falling from point Q to hitting the sea. loss in PE = mgh = 25 x 10 x 0.16 = 40J (1)

(iv)

Determine the speed with which the stone hits the sea. Total KE = 40J + 18J = 56J

KE = 12 mv 2

v=

2 KE m

v=

2 × 56 0.16

v = 27 ms −1 (2) (Total 7 marks)

2.4 Uniform circular motion 2.4.1 Draw a vector diagram to illustrate that the acceleration of a particle moving with constant speed in a circle is directed towards the centre of the circle. Objects perform uniform circulation motion when acted upon by a force towards the centre of the motion ( centripetal force) e.g. The only force on the Moon in its orbit is the pull of the Earth, which supplies the centripetal force.

2.4.2 Apply the expression for centripetal acceleration.

2.4.3 Identify the force producing circular motion in various situations. 2.4.4 Solve problems involving circular motion.

Topic 3.1 Thermal concepts 3.1.1 State that temperature determines the direction of thermal energy transfer between two objects. Temperature determines the direction of heat transfer. Heat always travels from hot to cold. When two objects are in contact with each other and at the same temperature, we say they are in thermal equilibrium. 3.1.2 State the relation between the Kelvin and Celsius scales of temperature. There are two temperature scales that can be used, the Kelvin scale and the Celsius scale. The relationship between then is T (K) = t (˚C) + 273

• 0ºC is the melting point of pure ice. • 0K is the absolute zero, the coldest temperature possible. • At 0k, the particles have no kinetic energy, it is practically and theoretically impossible to reach 0K but we can get close. • 0K is - 273.16ºC • The coldest temperature ever recorded was 700nK 3.1.3 State that the internal energy of a substance is the total potential energy and random kinetic energy of the molecules of the substance. The internal energy of a system is more commonly referred to as the Thermal Energy. Internal energy is the sum of kinetic and potential energy of the particles of a substance. The potential energy is due the energy stored in the bonds (bond energy) and the intermolecular force of attraction between particles. The kinetic energy is due to the translational, vibrational and rotational motion of the particles.

Allan Riddick

When you heat a substance, the particles more faster (increase KE.) and the bonds stretch (increase PE.) 3.1.4 Explain and distinguish between the macroscopic concepts of temperature, internal energy and thermal energy (heat) Temperature is a measure of the ‘hotness’ of something. In practice the temperature determines the direction of thermal energy transfer between a body at a higher temperature to a body at a lower temperature. At a microscopic level temperature is a measure of the average kinetic energy per molecule. The internal energy is sum total of the energy of all of the molecules in an object. The terms internal energy and thermal energy can be used interchangeably. 3.1.5 Define the mole and molar mass. The mole is the SI unit for the amount of a substance. The molar mass is the mass of one mole of a substance. 3.1.6 Define the Avogadro constant. 1 mole of a substance contains Avogadro’s number (6.02 x1023) of molecules 12g of carbon-12 contains 6.02 x1023 atoms.

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3.2 Thermal properties of matter 3.2.1 Define specific heat capacity and thermal capacity. Specific Heat Capacity is the amount of energy required to heat 1kg of a substance by 1ºC or 1K.

∆Q = cm∆T Where ∆Q c m ∆T

= Change in Heat Energy (J) = Specific Heat Capacity (Jkg-1K-1) = Mass (kg) =Change in temperature(K)

Thermal Capacity is amount of energy needed to change temperature of an object by 1ºC or 1K.

3.2.2 Solve problems involving specific heat capacities and thermal capacities.

3.2.3 Explain the physical differences between the solid, liquid and gaseous phases in terms of molecular structure and particle motion.

A solid is made up of particles that are arranged in a solid 3D shape. There is a strong force of attraction between the particles. If the solid was to be heated the particles would gain energy and start to vibrate more vigorously.

In a liquid the particles are free to move around. A liquid will mould itself to the shape of the container that it is in. There is still a force of attraction between the particles.

In a gas the particles are free to move around. The particles have a lot of energy so move quickly. Collisions between the molecules and the side of the container are responsible for the pressure which a gas exerts. There is almost no force of attraction between the molecules in a gas.

3.2.4 Describe and explain the process of phase changes in terms of molecular behaviour.

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Kinetic theory can be used to explain what happens to a substance as it is heated. To change form a solid to a liquid the particles must gain sufficient kinetic energy to overcome the forces between them and break away from their fixed positions. While the substance is changing state its temperature does not increase. This can be seen as a plateau (BC) when you look at a heating curve.

Once the phase change has been completed the particles begin to gain more kinetic energy and the temperature of the substance again increases. As the boiling point is increased the particles gain enough energy to completely overcome the intermolecular forces and escape into the gaseous state. As this happens there is another plateau in the cooling curve (D»E). Condensation: In condensation the particles are slowing themselves down becoming closer together and so forming water. Evaporation: The particles are heated together, they gain kinetic energy and when they gain enough energy they escape. Freezing: The particles lose kinetic energy and form a solid 3.2.5 Explain in terms of molecular behaviour why temperature does not change during a phase change. The energy is being used to break or make bonds and so the energy is not turned into kinetic energy.

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3.2.6 Distinguish between evaporation and boiling. Evaporation is the change of state from liquid to gas that occurs below the boiling point of that liquid. In a liquid a small amount of the molecules have sufficient kinetic energy to leave the surface of the liquid and become a gas. As the high energy molecules are leaving the liquid the temperature of the remaining liquid falls. The rate of evaporation depends on: • The surface area of the liquid. As molecules only leave from the surface of the liquid, if there is a large surface area then evaporation will occur more quickly. • The temperature of the liquid. If the liquid is warmer then more molecules will have sufficient Kinetic energy to escape. • The pressure of the air above the liquid. If the pressure is higher more Kinetic Energy will be required to escape. • Movement of air. If there is a draught across the liquid the rate of evaporation will increase. Boiling occurs when the whole liquid is heated to its boiling point. All the molecules have sufficient Kinetic Energy to turn into a gas. 3.2.7 Define specific latent heat. Latent heat of Vaporisation is the heat required to vaporise a unit of mass. Vaporisation is the technical term for the change in state between a liquid and a gas.

3.2.8 Solve problems involving specific latent heats. 3.2.9 Define pressure. Pressure is the force exerted per unit area. How is pressure exerted by a gas: Particles bounce off the walls of a container as they bounce their momentum changes. Momentum change/ time = Force Pressure = Force/ Area so pressure is exerted 3.2.10 State the assumptions of the kinetic model of an ideal gas. Kinetic theory uses the model of small particles bouncing around to describe the properties of gases (mainly) and matter in general. • Matter consists of large numbers of tiny particles • Particles are in constant motion moving in straight lines and thus have kinetic energy. • All collisions between particles and the sides of the container are elastic. • There are no forces between the particles of attraction or repulsion. • The average kinetic energy per particle is proportional to the Kelvin temperature of the gas. 3.2.11 State that temperature is a measure of the average random kinetic energy of the molecules of an ideal gas. Temperature is a measure of the average kinetic energy per particles of an ideal gas. 3.2.12 Explain the macroscopic behaviour of an ideal gas in terms of a molecular model. Boyle’s Law:

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Boyle's law states that at a constant temperature the volume of a gas increases when the pressure decreases. This is because the particles don’t lose kinetic energy and they collide more frequently against the walls.

p1V1 = p2V2 or pV = constant

Charles’ Law: At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature (in Kelvin) increases or decreases. This is because as temperature increases particles gain more kinetic energy which causes pressure to increase, hence volume increases as collisions increase.

V1 V2 = T1 T2 or

V = const. T Pressure Law: As temperature increases so does pressure this is because an increase in temperature the atoms will move faster and so they will collide more often the walls of a container and thus increasing the pressure.

p1 p 2 = T1 T2 or

p = const. T

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4.1 Kinematics of simple harmonic motion (SHM) 4.1.1 Describe examples of oscillations. Examples of Simple Harmonic Motion include: 1. Simple spring oscillator 2. Pendulum for small angles of oscillation 4.1.2 Define the terms displacement, amplitude, frequency, period and phase difference. Displacement

Distance from the equilibrium point

Amplitude

The maximum value for displacement from the mid point.

Frequency (f):

Period (T):

The number of oscillations per second measured in hertz (Hz) 1 Hz = 1 oscillation per second. The time taken for one oscillation measured in seconds.

T= Phase difference

1 f

A way of comparing two oscillations by finding the difference between their phases.

The two waves shown have a phase difference of 180°. This means that the first wave is half a wavelength in front of the second one.

4.1.3 Define simple harmonic motion (SHM) and state the defining equation as a = −ω2x. For an oscillation to be described as Simple Harmonic: • the force or acceleration is always directed to the centre of the motion. • the force or acceleration is proportional to the distance from the centre of motion 4.1.4 Solve problems using the defining equation for SHM. 4.1.5 Apply the equations v = v0 sin ωt, v = v0 cos ωt , v =±ω√(x02 − x2) , x = x0 cos ωt and x = x0 sin ωt as solutions to the defining equation for SHM. 4.1.6 Solve problems, both graphically and by calculation, for acceleration, velocity and displacement during SHM. Allan Riddick

4.2 Energy changes during simple harmonic motion (SHM) 4.2.1 Describe the interchange between kinetic energy and potential energy during SHM.

4.2.2 Apply the expressions EK= ½mω2(x02 – x2) for the kinetic energy of a particle undergoing SHM, ET= ½mω2x02 for the total energy and EP= ½mω2x2 for the potential energy. 4.2.3 Solve problems, both graphically and by calculation, involving energy changes during SHM.

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4.3 Forced oscillations and resonance 4.3.1 State what is meant by damping. Damping is a force that is always in the opposite direction to the direction of motion of the oscillating particle and that the force is a dissipative force. 4.3.2 Describe examples of damped oscillations. This happens on cars in their suspensions, when it vibrates the damper tries to reduce the number of oscillations, to reduce the possible effects. On a piano the pedals reduce the oscillations of the springs of the piano. One pedal reduces the damping and one cuts completely the oscillations. 4.3.3 State what is meant by natural frequency of vibration and forced oscillations. The natural frequency is the frequency that an object will oscillate at if it if moved from its equilibrium position and released. When a guitar string of a certain length is plucked it vibrates at a certain frequency. Objects can also be made to oscillate by an external force. This is known as forced oscillation. 4.3.4 Describe graphically the variation with forced frequency of the amplitude of vibration of an object close to its natural frequency of vibration.

4.3.5 State what is meant by resonance. If an object is forced to oscillate at its natural frequency resonance will occur. Resonance results in oscillations of a very large amplitude. 4.3.6 Describe examples of resonance where the effect is useful and where it should be avoided. Resonance can be a serious problem. When designing an aeroplane wing care must be taken that it will not resonate in flight.

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4.4 Wave characteristics 4.4.1 Describe a wave pulse and a continuous progressive (travelling) wave. 4.4.2 State that progressive (travelling) waves transfer energy. Waves transfer energy with no net movement in the medium they travel through. 4.4.3 Describe and give examples of transverse and of longitudinal waves.

Above is a diagram of a transversal wave. Transverse waves can be defined by the fact that they oscillate at right angles to the direction of energy transfer. Examples of such waves are ripples in the water of a pond, and vibrations along a taught rope.

Above is a diagram of a longitudinal wave. Examples of such waves are sound waves and compression waves down a spring. Note that these waves do not oscillate perpendicular to the ray or direction of energy transfer. 4.4.4 Describe waves in two dimensions, including the concepts of wavefronts and of rays. There are some important aspects of all waves which can be studied using the above. • Wave fronts – These are the movement of the wave pattern, i.e. when the curve is going up, or going down. The wave fronts highlight the parts of the waves which are moving together. • Rays – the rays highlight general direction of the wave and therefore the direction of the energy transfer. 4.4.5 Describe the terms crest, trough, compression and rarefaction. In the above we have seen various terms to describe features of waves, and below is a definition for these: • Crest – This is the highest point the wave oscillates, it is the top of the wave. This is a feature of a transversal wave. • Trough – The trough is the lowest point to which the wave oscillates, in other words it is the bottom of the wave. Again this is only a feature of transversal waves. • •

Compressions – This is the point in a longitudinal wave where everything is bunched together, i.e. there is high pressure. Rarefacations – This is the point where all the points are far apart and there is low pressure.

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4.4.6 Define the terms displacement, amplitude, frequency, period, wavelength, wave speed and intensity. Amplitude Period Frequency Wavelength Wavespeed Intensity

The amplitude is a measure of the maximum displacement of the wave. If there is no energy loss this value is constant. This is the time taken for one complete oscillation in seconds; this is also referred to as the periodic time. This is the number of oscillations that take place in one second, this is measured in hertz. 10Hz would mean that a wave is oscillating 10 times a second. This is the shortest distance between one oscillation this can be the distance between any two points as long as the two points are in the same position. This is the speed (in ms-1) at which the oscillation pass a stationary point. The intensity is the power per unit area that is absorbed by the observer. In English this is the power that the wave carries per oscillation to say as such, and is proportional to the square of the amplitude.

4.4.7 Draw and explain displacement–time graphs and displacement–position graphs for transverse and for longitudinal waves.

4.4.8 Derive and apply the relationship between wave speed, wavelength and frequency.

Wave Speed (ms-1) = Frequency (Hz) x wavelength (m) v = fλ

4.4.9 State that all electromagnetic waves travel with the same speed in free space, and recall the orders of magnitude of the wavelengths of the principal radiations in the electromagnetic spectrum.

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4.5 Wave properties 4.5.1 Describe the reflection and transmission of waves at a boundary between two media. At a boundary between two media, two things happen: • Reflection: In this case the law of reflection applies incident angle = reflected angle when measured from the normal ( an imaginary line at right angles to the surface). • Refraction: In this case the wave is refracted towards the normal entering a slower medium and away from the normal entering faster medium.

4.5.2 State and apply Snell’s law.

4.5.3 Explain and discuss qualitatively the diffraction of waves at apertures and obstacles. Diffraction is when the wave spreads out after passing through a narrow opening. In general, diffraction is greatest when the size of the opening is of the same order as the wavelength. 4.5.4 Describe examples of diffraction. • • •

Waves in the harbour, ocean waves diffract through the harbour opening and spread out. FM radio can be heard for a few meters after the tunnel opening as the signal diffracts through the opening. Light rays diffract around your hair so people with long floppy fringes can see diffraction patterns in bright weather.

4.5.5 State the principle of superposition and explain what is meant by constructive interference and by destructive interference. Superposition is when two waves meet and effect each other. The principle of superposition states that two waves add up in a vector fashion as follows:

This is called constructive interference and happens when the two waves are in phase. path difference = nλ

This is called destructive interference and happens when the waves are out of phase. Path difference = (n+½)λ

Allan Riddick

4.5.6 State and apply the conditions for constructive and for destructive interference in terms of path difference and phase difference. 4.5.7 Apply the principle of superposition to determine the resultant of two waves.

Allan Riddick

5.1 Electric potential difference, current and resistance 5.1.1 Define electric potential difference. The potential difference is defined as the work done per unit charge to move a positive test charge between A and B.

PotentialDifference =

EnergyDifference Ch arg e

The base unit for potential difference is the Joule per Coulomb (JC-1).

5.1.2 Determine the change in potential energy when a charge moves between two points at different potentials. To move a charge in an electric field work must be done. The change in the electrical potential energy (which is equal to the work done) is the potential difference.

When the charge, q, moves from point A to point B it gains electrical potential energy. Work must be done to move the charge. Change in potential energy = Force x distance =Fxd =Exqxd E is the Electric Field Strength and is explained further in Topic 6

5.1.3 Define the electronvolt. The joule is too large a measure of energy to be used at a subatomic level. For very small energies electronvolts (eV) are used. 1 eV = 1.6 x 10-19 J

5.1.4 Solve problems involving electric potential difference.

Allan Riddick

5.1.5 Define electric current. Electrical current is the flow of charged particles through a material when a potential difference is applied across it. By convention the current carriers are the positively charged particles. In a metallic conductor the charge carriers are electrons so the conventional current flows in the opposite direction to the charge carriers.

Electrical current is defined as the rate of flow of electrical.

Current =

I=

Ch arg e Time Q t

5.1.6 Define resistance. Resistance is a measure of how easily a charge can flow in a material. The resistance is defined as the ration of the potential difference across a material to the current flowing through it.

Re sis tan ce =

PotentialDifference Current R=

V I

The unit of resistance is the ohm (Ω). One ohm is defined as the resistance of a material through which a current of one amp flows when a potential difference of one volt is applied across it.

5.1.7 Apply the equation for resistance in the form R=ρl / A The resistance on a wire (at a constant temperature) depends upon • Length • Cross sectional area • Resistivity. The resistivity of a material tells us how well that material conducts. Good conductors have a very small resistivity (≈10-8 Ωm). Insulators have a very large resistivity (Glass ≈ 1012 Ωm) Allan Riddick

5.1.8 State Ohm’s law.

Ohm’s Law Providing the physical conditions such as temperature are kept constant, the resistance is constant over a wide range of applied potential differences and therefore the potential difference is directly proportional to the current.

Ohm’s law is commonly written as Voltage = Current x Resistance V=IR

5.1.9 Compare ohmic and non-ohmic behaviour. In non-ohmic behavior V and I are not proportional to each other. Examples of this include light bulb filaments and semi-conductor devises like diodes and transistors.

5.1.10 Derive and apply expressions for electrical power dissipation in resistors. Electrical power is the rate that an electrical devise uses energy.

P=

E V2 = I 2R = t R

5.1.11 Solve problems involving potential difference, current and resistance.

Allan Riddick

5.2 Electric circuits 5.2.1 Define electromotive force (emf). The emf is the amount of energy per unit charge supplied to a circuit by a power source. For a call it is the amount of chemical energy converted to electrical energy per unit charge..

5.2.2 Describe the concept of internal resistance. When a battery supplies a current to an external circuit it gets warm. This is due to the battery having a small internal resistance.

The Emf of the supply is the sum of the potential dropped across the internal resistor and the external resistor. ε = Ir + IR ε = Ir + Terminal Potential Terminal Potential = ε - Ir

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5.2.3 Apply the equations for resistors in series and in parallel. Resistors in Series

RTotal = R1 + R2 + …….

Resistors in Parallel

1 RTotal

=

1 1 + + ..... R1 R2

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5.2.4 Draw circuit diagrams

5.2.5 Describe the use of ideal ammeters and ideal voltmeters. Ammeters are used to measure the current in a circuit. They are connected in series with the component under test. In order to have no effect on the circuit they should have a very small resistance. Ideal ammeters have zero resistance. This means that no potential difference is dropped across them. Voltmeters are used to measure the voltage in the circuit. They are connected in parallel with the component under test. Voltmeters have a very high resistance so that very little current is allowed to flow through them. An ideal voltmeter has an infinite resistance.

Allan Riddick

5.2.6 Describe a potential divider. Resistors connected in parallel can be used to control voltages. By changing the ratio of the resistors it is possible to vary how much potential is dropped across either V1 or V2.

Vout = Vin

R2 R1 + R2

5.2.7 Explain the use of sensors in potential divider circuits. Light Switch

When light stops shining on the LDR then its resistance will increase. As the resistance changes the potential difference dropped across it will change. This change in potential can be detected by an external circuit which can then switch lights on and off as required.

Allan Riddick

Fields and forces This topic is best taught together so that the similarities and differences between the three types of field are discussed. Fields are regions of space in which susceptible particles feel a force: • A gravitational field is a region of space in which a mass feels a force because of gravity. • An electrical field is a region of space in which a charge feels a force because of another nearby charge. • A magnetic field is a region of space where magnetic materials experience a force. These three types of fields are studied together because they have similarities and the techniques for performing calculations are similar too, but there are also significant differences: • • •

Gravity is always attractive and there is only one type of mass. Electric forces can be attractive or repulsive and we can have negative or positive charge. Magnetic forces can also be attractive or repulsive and there are two types of magnetic pole (North and South) these always appear in pairs.

6.1 Gravitational force and field 6.1.1 State Newton’s universal law of gravitation. Every point mass attracts every other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses:

F=

GMm r2

Where F is the magnitude of the gravitational force between the two point masses, G is the gravitational constant, M is the mass of the first point mass, m is the mass of the second point mass, r is the distance between the two point masses.

6.1.2 Define gravitational field strength. A gravitational field is a region of space in which a mass feels a force because of gravity. Gravitational field strength is the force per unit mass on a particle because of the gravitational field.

g=

F m

Where g is the gravitational Field strength in NKg-1 F is the force experienced in N m is the mass of the object in kg 6.1.3 Determine the gravitational field due to one or more point masses. Field strengths are vectors and therefore the gravitational field due to one or more point masses can be found by vector addition. Allan Riddick

61.4 Derive an expression for gravitational field strength at the surface of a planet, assuming that all its mass at concentrated at its centre. The gravitational field strength at the surface of planet is more commonly known as “little g” or g (at the surface of the Earth it is 9.8 NKg-1) The force experienced by a mass in a gravitational field is given by

F=

GMm r2

And the gravitational field strength is defined as

g=

F m

By combining these formulas the gravitational field strength due to a point mass is given by

g=

GM r2

Allan Riddick

6.2 Electric force and field 6.2.1 State that there two types of electric charge There are two types of electric charge. Positive and Negative

6.2.2 State and apply the law of conservation of charge. Charge can be added or removed from an object but it cannot be destroyed. Charge conservation is the principle that electric charge can neither be created nor destroyed. The quantity of electric charge is always conserved. 6.2.3 Describes and explain the difference in the electrical properties of conductors and insulators. Conductors allow electric charges to pass through them. In a metallic conductor the charges that flow are electrons. An insulator is a material that does not allow charges to flow. 6.2.4 State Coulomb’s law. Coulombs law is used to calculate the force of attraction or repulsion between two point charges.

F=

q1 q 2 4πε 0 r 2

Where F is the magnitude of the force between the two charges in Newtons ε0 is the permittivity of free space - 8.85x10-12 C2N-1m-2 q1 is the charge of the first point charge in Coulombs, q2 is the charge of the second point charge in Coulombs, r is the distance between the two point charge in meters. 6.2.5 Define electric field strength. Electric field strength is defined as the force experienced per coulomb by a small positive charge in an electric field.

E=

F q

Where E is the electric field strength in NC-1 F is the force experienced but the charge in N q is the charge on the object in C. The electric field strength close to a sphere can be derived in the same way as gravitational field strength to be:

E=

q 4πε 0 r 2

6.2.6 Determine the electric field strength due to one or more point charges.

Allan Riddick

Field strengths are vectors and therefore the electric field due to one or more point charges can be found by vector addition. 6.2.7 Draw the electric field patterns for different charge configurations.

Field lines around a charged sphere

Field lines due to a dipoles

Field lines due to parallel plates The region between a set of parallel plates is a uniform electric field. The field lines are parallel and equally spaced telling us that the electric field strength is constant. 6.2.8 Solve problems involving electric charges, forces and fields.

Allan Riddick

6.3 Magnetic force and field 6.3.1 State that moving charges give rise to magnetic fields. When an electric current flows through a wire a magnetic field is created. 6.3.2 Draw magnetic field patterns due to currents.

The direction of the field lines surrounding a wire can be found using a right hand rule. The magnetic field caused by the current can be increased by coiling the wire, creating a solenoid.

6.3.3 Determine the direction of the force on a current-carrying conductor in a magnetic field. When a current carrying wire is placed between the poles of a magnet it experiences a force. This force causes the wire to “jump”

The direction that the wire will jump can be predicted using Fleming Left Hand Rule. Line your thumb, first and second fingers as shown below.

Allan Riddick

6.3.4 Determine the direction of the force on a charge moving in a magnetic field.

F = BIl Where F is the force experienced by the wire, measured in Newtons B is the magnetic field strength, measured in Tesla I is the current flowing through the wire, measured in Amps l is the length of wire between the poles of the magnet, measured in Meters.

6.3.5 Define the magnitude and direction of a magnetic field.

6.3.6 Solve problems involving magnetic forces, fields and currents.

Allan Riddick

7.1 The atom

7.1.1 Describe a model of the atom that features a small nucleus surrounded by electrons. Facts and figures about the atom. Diameter of a nucleus Diameter of an atom Mass of nucleus Mass of a proton Mass on an neutron Mass of an electron Charge on a proton Charge on an electron

≈10-15m ≈10-10m ≈10-27kg 1.673×10−27 kg 1.675×10−27 kg 9.110×10−31 kg -1.60x10-19C -1.60x10-19C

7.1.2 Outline the evidence that supports a nuclear model of the atom. The best evidence for the nuclear model of the atom is the Geiger-Marsden Gold leaf experiment. They fired a beam of charged particles at a single layer of gold molecules and observed what happened. According to the JJ Thomson “Plum Pudding” model they were expecting the charged particles to pass straight through.

They were very surprised that some of the alpha particles where deflected as they passed through the gold. From this they deduced that there the atom was made up of a small massive positively charged nucleus surrounded by space.

7.1.3 Outline one limitation of the simple model of the nuclear atom. The problem with this theory was that accelerating charges are known to lose energy. If the orbiting electrons were to lose energy they would spiral into the nucleus. The Rutherford model cannot explain to us how atoms are stable.

Allan Riddick

7.1.4 Outline evidence for the existence of atomic energy levels. This model was developed further by Niels Bohr. He suggested that the electrons orbit the nucleus rather like a planet orbits the sun. The radius of Bohr’s electrons depended on the energy they had. He also suggested that they could only move in certain orbits.

When the electrons moved from a high energy state to a lower energy state they emitted a photon of light. The frequency of the light depends on the difference between the energy levels.

hf = E1-E2 Where h f E1 E2

Planks constant (6.02 x 10-34 m2 kg s-2) Frequency of the emitted photon (Hz) Energy level before emitting photon (J) Energy level after photon has been emitted (J)

As there are a fixed number of energy levels only a few wavelengths of light are given out. This results in a line spectrum. Each individual element has distinct energy levels and therefore the emission spectra can be used to identify them.

Nuclear structure 7.1.5 Explain the terms nuclide, isotope and nucleon. Nuclide – protons and neutrons that form a nucleus Isotope – nuclei that have the same number of protons but a different number of neutrons. Nucleon – The collective name for particles that are found in the nucleus (protons and Neutrons) Allan Riddick

7.1.6 Define nucleon number A, proton number Z and neutron number N. Nucleon Number, A – The number of protons and neutrons that are in the nucleus. Proton Number, Z – The number of protons that are in the nucleus. Neutron Number, N – The number of neutrons that are in the nucleus.

7.1.7 Describe the interactions in a nucleus. According to our knowledge of electrostatics a nucleus should not be stable. Protons are positive charges so should repel each other. There must be another force in the nucleus that overcomes the electrostatic repulsion and hold the nucleus together. This force is called the strong nuclear force. Strong nuclear forces must be very strong to overcome the electrostatic forces. They must also have a very small range as they are not observed outside of the nucleus. Neutrons have some involvement in strong nuclear forces. Small nuclei have equal numbers of protons and neutrons. Larger nuclei, which are harder to hold together, have a greater ratio of neutrons to protons.

Allan Riddick

7.2 Radioactive decay 7.2.1 Describe the phenomenon of natural radioactive decay. 7.2.2 Describe the properties of alpha and beta particles and gamma radiation. 7.2.3 Describe the ionizing properties of alpha and beta particles and gamma radiation. 7.2.4 Outline the biological effects of ionizing radiation. 7.2.5 Explain why some nuclei are stable while others are unstable. Half-life 7.2.6 State that radioactive decay is a random and spontaneous process and that the rate of decay decreases exponentially with time. 7.2.7 Define the term radioactive half-life. 7.2.8 Determine the half-life of a nuclide from a decay curve.

7.3 Nuclear reactions, fission and fusion Nuclear reactions 7.3.1 Describe and give an example of an artificial (induced) transmutation. 7.3.2 Construct and complete nuclear equations. 7.3.3 Define the term unified atomic mass unit. 7.3.4 Apply the Einstein mass–energy equivalence relationship. 7.3.5 Define the concepts of mass defect, binding energy and binding energy per nucleon. 7.3.6 Draw and annotate a graph showing the variation with nucleon number of the binding energy per nucleon. 7.3.7 Solve problems involving mass defect and binding energy. Fission and fusion 7.3.8 Describe the processes of nuclear fission and nuclear fusion. 7.3.9 Apply the graph in 7.3.6 to account for the energy release in the processes of fission and fusion. 7.3.10 State that nuclear fusion is the main source of the Sun’s energy. 7.3.11 Solve problems involving fission and fusion reactions. Allan Riddick

Allan Riddick

8.1 Energy degradation and power generation 8.1.1 State that thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system. 8.1.2 Explain what is meant by degraded energy. The second law of thermodynamics states that “it is impossible to take heat from a hot object and use it without losing some heat to the surroundings”. Energy becoming more spread out is known as the degradation of energy. Whenever thermal energy is converted into mechanical energy some of the energy is degraded (lost) to the environment. 8.1.3 Construct and analyse energy flow diagrams (Sankey diagrams) and identify where the energy is degraded. Sankey diagram for a petrol engine.

8.1.4 Outline the principal mechanisms involved in the production of electrical power. Mechanical energy can be converted into electrical energy using a generator of dynamo. A coil is turned in a magnetic field. As the coil cuts the field lines, electrons move round the coil. The movement of electrons causes a potential difference which results in a current flowing. A current has been induced in the coil. A more detailed explanation of electromagnetic induction can be found in Unit 12, Electromagnetic induction.

Allan Riddick

8.2 World energy sources 8.2.1 Identify different world energy sources. Modern society requires a lot of energy. Most of the energy recourses used by humans hum are used to make electricity or to make things move. 8.2.2 Outline and distinguish between renewable and non-renewable non renewable energy sources. A renewable source of energy cannot be used up. A non-renewable non renewable source of energy can be used up and will eventually run out. Renewable Energy Solar Wind Hydroelectric Wave Tidal Biofuels (Wood, ethanol) Geothermal

Non-Renewable Energy Coal Oil Gas Nuclear (Uranium)

8.2.3 Define the energy density of a fuel. Energy density is the amount of energy that can can be obtained per kilogram of fuel.

8.2.4 Discuss how choice of fuel is influenced by its energy density. The cost of transporting fuels is dependent on the fuel density. A fuel with a low fuel density will be expensive to transport.

Allan Riddick

8.2.5 State the relative proportions of world use of the different energy sources that are available. Worldwide Energy resources

8.2.6 Discuss the relative advantages and disadvantages of various energy sources.

Allan Riddick

8.3 Fossil fuel power production A fossil fuel fired power plant is and based on somewhat ancient methods of energy production. The fossil fuel is placed in a combustion chamber and burnt to produce heat. In order to turn the heat energy to electric energy, water is pumped around the combustion chamber and the heat from the chamber heats the water and it turns to steam. In the case of a coal fired plant this heats the water to 1000ºC. The steam is used to turn a turbine which is attached to a generator. The generator generates converts the kinetic energy into electrical energy. Meanwhile the used steam goes to a condenser where it is cooled and turns to liquid water again; this lets off the big clouds often seen coming from these power plants. These clouds are nothing more than steam. The water is then pumped back into the combustion chamber to begin the cycle again. Coal Fired Power Station

8.3.1 Outline the historical and geographical reasons for the widespread use of fossil fuels. 8.3.2 Discuss the energy density of fossil fuels with respect to the demands of power stations. 8.3.3 Discuss the relative advantages and disadvantages associated with the transportation and storage of fossil fuels. 8.3.4 State the overall efficiency of power stations fuelled by different fossil fuels. 8.3.5 Describe the environmental problems associated with the recovery of fossil fuels and their use in power stations.

Allan Riddick

8.4 Non-fossil Non fuel power production Nuclear power

8.4.1 Describe how neutrons produced in a fission reaction may be used to initiate further fission reactions (chain reaction). In a nuclear reactor a large nuclei, e.g. Uranium-236, Uranium 236, is bombarded with a neutron and splits spl into two smaller nuclei. The daughter nuclei have less mass than the parent and so energy is released.

During the reaction two or 3 neutrons are released. They can move on and collide with other uranium nuclei and create a chain reaction. A chain chain reaction will only occur if the neutrons are slowed down by a moderator and if there is a large enough piece of fissional material. The minimum amount of material needed for a chain reaction to take place is called the critical mass. 8.4.2 Distinguish between controlled nuclear fission (power production) and uncontrolled nuclear fission (nuclear weapons). In a nuclear power station it is important that the chain reaction is controlled. Only one neutron from each reaction can be allowed to make fission. fission. The other neutrons are absorbed by control rods in the reactor. In a nuclear weapon the chain reaction is not controlled. The fissionable material and a moderator are mixed together. 8.4.3 Describe what is meant by fuel enrichment. Allan Riddick

99.3% of the uranium dug out of the ground is Uranium-238. Uranium-238 will absorb neutrons but will not fission so its presence in a nuclear reactor can hinder the chain reaction. The fuel in the reactor (or weapon) needs to have a much higher concentration of Uranium-235. The raw uranium must be enriched before it can be used. Commercial reactors use fuel with 5% Uranium-235. Weapon grade Uranium has over 85% Uranium-235. 8.4.4 Describe the main energy transformations that take place in a nuclear power station.

8.4.5 Discuss the role of the moderator and the control rods in the production of controlled fission in a thermal fission reactor. Moderator

The moderator slows down the neutrons. If the neutrons have too high an energy they will pass straight thorough the uranium nuclei and fission will not occur.

Control Rods Control rods are raised and lowered in the reactor to control the rate of fission. 8.4.6 Discuss the role of the heat exchanger in a fission reactor. The whole reactor is housed within a large pressure vessel. Pressurised gas is passed through the reactor core and then takes the heat out to a heat exchanger. The heat exchanger heats up water turning it into steam. This steam is used to turn a turbine which is connected to a generator. The steam is cooled down in a condenser and then recirculated. 8.4.7 Describe how neutron capture by a nucleus of uranium-238 (238U) results in the production of a nucleus of plutonium-239 (239Pu). 8.4.8 Describe the importance of plutonium-239 (239Pu) as a nuclear fuel. 8.4.9 Discuss safety issues and risks associated with the production of nuclear power. 8.4.10 Outline the problems associated with producing nuclear power using nuclear fusion. 8.4.11 Solve problems on the production of nuclear power. Solar power 8.4.12 Distinguish between a photovoltaic cell and a solar heating panel. A photovoltaic cell converts solar radiation directly into a voltage. Solar Heating panels absorb solar radiation and use it to heat water. This water can be used domestically and saves energy by reducing the amount of fuel being used for heating. 8.4.13 Outline reasons for seasonal and regional variations in the solar power incident per unit area of the Earth’s surface. 8.4.14 Solve problems involving specific applications of photovoltaic cells and solar heating panels. Hydroelectric power 8.4.15 Distinguish between different hydroelectric schemes. This form of renewable energy probably is the most simple of them all in terms of the concepts and science involved. The kinetic energy of water moving downhill is being used to turn a turbine which is attached to a generator. The generator turns the kinetic energy into electrical energy. A diagram of this basic model is shown below. Allan Riddick

A large store of water must be created creat for this method to be viable. Constantly onstantly produce an elevated power output means that a reservoir must be created. This his causes the problem of an area of land having to be flooded in order to create the reservoir, reservoir this can cause ecological problems. These problems are often overlooked as the amounts of energy produced are massive. massive power is currently the only widely used renewable energy source.

Hydroelectric

8.4.16 Describe the main energy transformations that take place in hydroelectric schemes.

8.4.17 Solve problems involving hydroelectric schemes. Wind power 8.4.18 Outline the basic features of a wind generator. Wind power relies on the conversion of kinetic energy in the wind into electrical energy using turbines. There is a great deal of kinetic energy in the wind. Different parts of the atmosphere are heated to different temperatures. The temperature differences causes pressure differences, due to hot air rising risi or cold air sinking, which result in air flows. flows

There are some advantages and disadvantages of the use of wind power. The advantages are that it’s a very ‘clean’ production, it is renewable and the source of energy is free. The disadvantages are that the source of energy is unreliable able as there could be a day without wind, it has a low energy density, it can be seen as visual pollution as it spoils the countryside, it can be noisy and the best positions for wind are usually far away from centers of population. population

8.4.19 Determine the power that maybe delivered by a wind generator, assuming that the wind kinetic energy is s completely converted into mechanical kinetic energy, and explain why this is impossible. 8.4.20 Solve problems involving wind power. Wave power 8.4.21 Describe the principle of operation of an oscillating water column (OWC) ocean-wave ocean energy converter. Allan Riddick

Wave power uses the kinetic energy of waves to generate electrical energy. One of the successful techniques is using the oscillating water column (OWC). The OWC is a device built on land. In-coming waves force air in and out of a turbine, which generates electrical energy. The particular design of the turbine (Wells turbine) means of that it generates electrical energy whatever the direction of flow of the air. 8.4.22 Determine the power per unit length of a wavefront, assuming a rectangular profile for the wave. 8.4.23 Solve problems involving wave power.

Allan Riddick

8.5 Greenhouse effect Solar radiation 8.5.1 Calculate the intensity of the Sun’s radiation incident on a planet. 8.5.2 Define albedo. Albedo is the term used to describe the ratio of reflection to absorption for an object. The Albedo for a white shiny object is high. Snow reflects most of the radiation incident on it and has an Albedo of around 90%. The average Albedo for the earth is about 30%. 8.5.3 State factors that determine a planet’s albedo. There are a number of factors which affect a planet’s albedo: Firstly the albedo varies across the surface of the planet due to: • Land coverage i.e. land or water or snow • Vegetation coverage • Latitude • Time of year (Because it affects the vegetation)

The greenhouse effect 8.5.4 Describe the greenhouse effect. The greenhouse effect consists of the earth receiving short wave-length radiation from the sun, and this then causes the surface to warm up. The Earth will then emit infra-red radiation (longer wavelengths than absorbed, because the earth is cooler. Some of this outgoing radiation is intercepted and absorbed by the greenhouse gases and after which it is re-radiated in all directions. If the energy radiated and the energy absorbed is equal the temperature of the planet will remain constant. But that isn’t happening at the moment more energy is absorbed than radiated, and so the earth gets warmer. Truck Analogy of the Greenhouse Effect If only 10% of the greenhouse gases are radiated from the Earth, then the Earth supposedly should be heating up but it’s not. So why is this so? Well, we could use an analogy of a truck delivering sand. Each time it delivers 100kg of sand, and 10% of the sand at the drop of point is carried away. At the beginning the amount of sand increases rapidly seeing as more is brought in then taken out. But eventually those 10% taken out will be equal to the 100kg brought in and the load would stabilize. The same is true for the earth’s temperature. A graph is shown below of this effect.

Load against Time 1000 800 600 400

Load (kg)

200 0 0

20

40

60

80

8.5.5 Identify the main greenhouse gases and their sources. Allan Riddick

The Greenhouse Gases that occur in the earth’s atmosphere are: • Methane • Water • Carbon Dioxide Combustion of fossil fuels releases this gas into the atmosphere and it has a very important role in the greenhouse effect. It is naturally removed from the atmosphere by Carbon Fixation by plants in photosynthesis. • Nitrous Oxide nd industries are big producers of this and it has a significant effect as it can remain Livestock and in the upper atmosphere for a long time as it is harder to “fixate”. • Ozone This is responsible for absorbing high energy UV photons which could be harmful to living organisms. However these can be changed in their ratios due to human industry and technology.

8.5.6 Explain the molecular mechanisms by which greenhouse gases absorb infrared radiation. Each of these gases absorbs certain wavelengths of the electromagnetic electromagnetic waves emitted by the sun. They do as a result of resonance. The natural frequency of the oscillation of the bonds within the molecules of the gas in within the infrared region. If the driving frequency (from the radiation emitted by the Earth) is equal to the natural frequency of the molecule, resonance will occur. The amplitude of the molecules’ vibrations increases and the temperature increases. The absorption will take place at specific frequencies depending on the molecular bonds. 8.5.7 Analyse absorption rption graphs to compare the relative effects of different greenhouse gases. Below is an absorption spectrum graph for each of the greenhouse gases, thus showing that each gas absorbs a different wavelength of radiation.

8.5.8 Outline the nature of black ck-body radiation. 8.5.9 Draw and annotate a graph of the emission spectra of black bodies at different temperatures. Black objects are the best absorbers and radiators of radiation. The range of wavelengths emitted for a black body emitter is shown below. The peak of the graph represents the most intense wavelength.

Allan Riddick

The peak wavelength can be calculated using Wien’s Law. Wien’s Law ߣ௠௔௫ = Where λmax T B

ܾ ܶ

Wavelength of maximum intensity Temperature of black body constant = 2.89 x 10-3 mK

8.5.10 State the Stefan–Boltzmann law and apply it to compare emission rates from different surfaces. The Stefan-Boltzmann law relates the total energy emitted per unit area by a black body emitter to its temperature. Stefan-Boltsmann Law ܲ‫ ܶߪ = ܽ݁ݎܽ ݐ݅݊ݑ ݎ݁݌ ݎ݁ݓ݋‬ସ Where σ = 5.67 x 10-8 W m-2 K-4 8.5.11 Apply the concept of emissivity to compare the emission rates from the different surfaces. The surface of the earth is not a perfect black body emitter. Emissivity compares the rate at which a body radiates energy to the rate at which a black body emitter at the same temperature emits radiation.

ε=

Power emitted by object per unit area Power radiated by a black body at the same temperature

8.5.12 Define surface heat capacity Cs. The surface heat capacity is the energy that is required to raise 1m3 of the surface of a planet by 1°C. 8.5.13 Solve problems on the greenhouse effect and the heating of planets using a simple energy balance climate model.

Allan Riddick

8.6 Global warming Global warming 8.6.1 Describe some possible models of global warming. 8.6.2 State what is meant by the enhanced greenhouse effect. The enhanced greenhouse effect is believed to be caused by the increase in production of greenhouses gases by humans. 8.6.3 Identify the increased combustion of fossil fuels as the likely major cause of the enhanced greenhouse effect. Combustion of fossil fuels releases carbon dioxide into the atmosphere. The use of fossil fuels increased significantly during the second half of last century. This resulted in a increase in the amount of carbon dioxide in the atmosphere and is believed to have resulted in an increase in the average temperature of the earth. 8.6.4 Describe the evidence that links global warming to increased levels of greenhouse gases. 8.6.5 Outline some of the mechanisms that may increase the rate of global warming. 8.6.6 Define coefficient of volume expansion. The coefficient of volume expansion tells us the change in volume of a substance per degree change in temperature.

Δܸ ܸ଴ ΔΘ coefficient of volume expansion measured in K-1 increase in volume measured in m3 initial volume of water measured in m3 increase in temperature measured in K Υ=

Where γ ∆V Vo ∆Θ

8.6.7 State that one possible effect of the enhanced greenhouse effect is a rise in mean sealevel. If the average temperature of the oceans is caused to rise then the mean sea level will rise. In the past 100 years the mean sea level has risen by 20cm. The rate that the sea level will rise is difficult to predict due to the difficulty in accurately measuring the volume increase of water. Water that is between 0 and 4°C has a negative volume coefficient so at these temperatures it will contract as it warms. Another factor is the ice that covers the land. As this melts it will run into the sea causing the levels to rise by an unknown amount. Melting glaciers will have little effect on sea levels as they already displace their own mass of water. 8.6.8 Outline possible reasons for a predicted rise in mean sea-level. 8.6.9 Identify climate change as an outcome of the enhanced greenhouse effect. Global warming will cause changes to the climate. Models predict that it will become warmer closer to the equator and wetter in the northern hemisphere. Some models predict that as there is more energy in the atmosphere storms will become more frequent and powerful. Allan Riddick

8.6.10 Solve problems related to the enhanced greenhouse effect. 8.6.11 Identify some possible solutions to reduce the enhanced greenhouse effect. Reduction in the consumption of fossil fuels would reduce the enhanced greenhouse effect. Strategies include: • Changing human activities that cause pollution o Using energy saving light bulbs o Improving efficiency of energy production o Using electric and hybrid vehicles o Replace fossil fuels with renewable or nuclear energy • Reducing the pollutants at the point of emission o Capture carbon dioxide and store it underground o Reduce methane emission from cows by diet • Clean up and restoration o Plant more trees to act as a carbon sink o Add iron to oceans to remove carbon dioxide from the air

8.6.12 Discuss international efforts to reduce the enhanced greenhouse effect. IPCC

International Panel on Climate Change The IPCC was established to provide the decision-makers and others interested in climate change with an objective source of information about climate change. The IPCC does not conduct any research nor does it monitor climate related data or parameters. Its role is to assess on a comprehensive, objective, open and transparent basis the latest scientific, technical and socio-economic literature produced worldwide relevant to the understanding of the risk of human-induced climate change, its observed and projected impacts and options for adaptation and mitigation. http://www.ipcc.ch

Kyoto Protocol

“The Kyoto Protocol is a legally binding agreement under which industrialized countries will reduce their collective emissions of greenhouse gases by 5.2% compared to the year 1990 (but note that, compared to the emissions levels that would be expected by 2010 without the Protocol, this target represents a 29% cut). The goal is to lower overall emissions from six greenhouse gases - carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, HFCs, and PFCs calculated as an average over the five-year period of 2008-12. National targets range from 8% reductions for the European Union and some others to 7% for the US, 6% for Japan, 0% for Russia, and permitted increases of 8% for Australia and 10% for Iceland." http://www.kyotoprotocol.com

APPCDC

Asia-Pacific Partnership on Clean Development and Climate APP partners Australia, Canada, China, India, Japan, Korea, and the United States have agreed to work together and with private sector partners to meet goals for energy security, national air pollution reduction, and climate change in ways that promote sustainable economic growth and poverty reduction. The Partnership will focus on expanding investment and trade in cleaner energy technologies, goods and services in key market sectors. http://www.asiapacificpartnership.org

Allan Riddick