(Phys)Compiled Definitions and Principles for ASlevel paper 1/Paper 2

TERMINOLOGY AND PRINCIPLES Measurements Base Quantities- physical quantities that cannot be broken down any further Derived Quantities- physical quantities that are obtained by combining the base quantities i.e. can be expressed as product or quotient of other physical quantities. Scalar quantities – has magnitude only. Vector Quantities – has magnitude and direction. Systematic Errors (AS) – all readings have the same error • Errors which will result the scattered equally about the true value; • Can be reduced (but never eliminated) by averaging • Error is due to observer Kinematics Distance – total length along a specified path Displacement – Distance moved from a fixed point in a specified direction. Speed – rate of change of distance Velocity – rate of change of displacement Acceleration – rate of change of velocity Note: Projectile motion For any projectile • Its VERTICAL motion is at constant ACCELERATION • Its HORIZONTAL is at constant SPEED Linear momentum - product of mass and velocity of an object and it acts in the same direction as the velocity Newton’s Laws • FIRST LAW – An object will remain at rest or continue to move in a constant velocity unless acted upon by an external resultant force. • –

SECOND LAW Rate of change of momentum of a body is directly proportional to the external resultant force acting upon it and it occurs in the direction of the force.

Rate of momentum α F

(mv - mu) α F t m(v - u) α F t ma α F F= kma , k =1 F = ma • –

THIRD LAW If body A exerts a force on body B then body B exerts equal but opposite in direction to force on body A

Force, Energy and Equilibrium Mass – Measure of Body’s reluctance to change in its state of motion (i.e. its inertia). (Constant and a scalar quantity) Weight – Gravitational force acting on the object. (A vector quantity) Centre of Gravity – Point of which the whole weight of the body acts upon. Centre of Mass – Point through which an applied force causes no rotation. Principle of Conservation of Momentum – The total momentum of a system remains constant provided that no external force acts upon the system (isolated system). *Applies for both elastic and inelastic collision as well as explosion Upthrust – caused by the pressure that the fluid exerts on the object (on the top and the bottom of an object) – It is due to the difference in fluid pressure between the top and the bottom of the object. – Acts vertically upwards – (Archimedes’ Principle) Equal to the weight of the fluid displaced when a body is wholly or partially immersed in a fluid. ➢ For an object immersed in a fluid the buoyancy force is equal to the weight of the fluid displaced – Can be applied generally of not just when the object has a regular shape. ➢ An object floats in water because the buoyancy force on it is equal and opposite in direction to its weight. For a body to be in equilibrium ➢ Resultant force is zero in any direction (closed triangle) ➢ Resultant moment or torque is zero about any point. ➢ Stationary or move in a constant velocity

Moment of the force – is the product of the force and the perpendicular distance of the line of action of the force from the pivot. Couple – consists of two equal and opposite forces whose lines of actions do not coincide. Torque of a couple – is the product of one of the forces and the perpendicular distance between the forces. (No linear acceleration) -therefore producing a turning effect. The Principle of Moments – states that for a body to be in rotational equilibrium the sum of the clockwise moments about any point must be equal to the sum of anticlockwise moments about the same point. Work – product of force and the distance moved in the direction of force. Energy – stored ability to do work. Kinetic energy – is the stored ability to do work due to its motion. Potential energy – is the stored energy available to do work due to its position or shape. Principle of conservation of energy – Energy may be transferred from one form to another but it cannot be created nor is destroyed i.e. total energy of an isolated system constant. Power – work done per unit time Electric Fields Electric field – is a region of space where a charge experiences a force. Direction of electromagnetic field – is the direction in which a positive charge would move if it were free to do so. – Shows the direction of force on the positive charge. Electric field strength – Force per unit positive charge placed at a point. • The closer the magnetic field the stronger it is. Electric Circuits Electric current – is the rate of flow of charged particles. Conventional current – flows from the positive terminal of the battery to the negative terminal (form a high potential to a low potential) i.e. in the direction of flow of positive charge. Flow of electrons – is from the negative terminal of the battery to the positive terminal (form a low potential to a high potential) i.e. in the direction of flow of electrons. Direct Current – direction of current is fixed.

Alternating current – motion of electric charges is periodically reversed. Potential Difference – amount of electrical energy transferred to other forms of energy when unit charge passes between two points. Electromotive force - amount of energy transferred from other forms of energy to electrical energy by a source in driving unit charge around a complete circuit. Resistance – ratio of potential difference across a component to the current in it. Ohm’s Law – current through a conductor is directly proportional to the potential difference across it provided that temperature is constant. Resistivity – is numerically the resistance of a sample unit length and the cross sectional area at a certain temperature. Kirchoff’s Laws –

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• FIRST LAW (CONSERVATION OF CHARGE) Charge entering each second = Charge leaving each second (I.e. charge cannot be created nor destroyed) • SECOND LAW (CONSERVATION OF ENERGY) In any closed circuit or loop the sum of electromotive force is equal to the sum of potential difference.

Radioactivity Proton number – is the number of protons in the nucleus of the atom. Nucleon number – is the total number of protons and neutrons in the nucleus of the atom. Relative Atomic Mass – ratio of mass of an atom to 1/12 mass of a C-12 atom (unit u) Isotopes – atoms with the same proton number but different nucleon number. ➢ Isotopes have the same chemical properties as they have the same number of electrons but have slightly different mass. Nuclide – an atom of a particular nuclear structure. Nuclear Reaction – nucleus may be transmuted to a different nucleus by bombarding it with high energy particles. Nuclear Radiation – 3 types of radiation: α-particles, β-particles, γ-particles. Note: Principle of Conservation of Charge and Nucleons -

In radioactive decay (nuclear processes) the charge and the number of nucleons are the same before and after decay. Note: Principle of Conservation of Energy (Energy cannot be created nor destroyed) -mass and energy is equivalent (E=mc) in any nuclear processes. Radioactive decay –is the process by which unstable nuclei become more stable by emitting α or β – particles or γ radiation. Spontaneous decay – rate of decay is unaffected by environmental changes e.g. temperature. Random decay – cannot predict which particular nucleus decay next – Constant probability of decay per unit time of a nucleus. Background Radiation – consists of cosmic rays, particles emitted by radioactive carbon in the atmosphere – E.g. radon gas, radiation from rocks and etc... Background count – Even in the absence of radioactive source, the GM tube will register some counts it is caused by background radiation. Fusion – Light atoms fuses together to make heavier atoms which can only occur if energy is released. – (Source of energy from the Sun and stars) Fission – heavy atoms is broken into two roughly equal parts then energy is released. – (Used in nuclear power station) Mass defect – is the difference between the mass and its constituent’s particles taken separately and the mass of the atom itself. • •

Iron has the greatest mass defect thus it is the most abundant element. Theory: atom which has a high mass defect has a great deal of work to be done on it in order to separate into it’s constituent nucleons (in a low energy state)

Binding energy – is the work done to separate the atom into several individual protons, electrons and neutrons. Half – life – the average time it takes for half of the atoms of any nuclide to decay. Nucleon - a proton and nucleon The activity of a radioactive isotope – is the number of disintegrations per second. Phases of Matter Density – mass per unit volume Brownian motion – is the random movement of smoke particles.

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Observation – smoke particles scatter the light shining on them and so tiny specks of lights can be observed Explanation – irregular random movement of the smoke particles is due to uneven bombardment of invisible air molecules and the smoke particles. (Produces a resultant force which is not constant but rapidly changing • Air molecules are constantly moving in rapid, random and continuous motion.

Scenario: • If large smoke particles were used. – There will be less haphazard movement because the randomness of the invisible air molecules and the smoke particles would be ‘averaged out’. Melting - process by which matter changes from solid to liquid at a constant temperature (melting point) on hearting. Boiling – process by which matter changes from liquid to gas at a constant temperature (the boiling point) on heating. The heat supplied (the latent heat of fusion) -may increase the EP of molecules while average EK of molecules remain fairly constant (as temperature is constant) The heat supplied (the latent heat of vaporisation) – increases the EP of molecules and enables the molecules to do work in pushing back the external pressure. Evaporation – process by which liquid changes into water vapour without boiling i.e. at any temperatures below its boiling point. • More energetic water molecules escape from the surface of the liquid, leaving behind the less energetic ones • So the average EK of the remaining molecules will decrease • Temperature depends on the average EK of the molecules • Since the average EK decreases, the temperature of the liquid will drop and the liquid cools down thus causes cooling. Rate of evaporation depends on • The surface area of the liquid • The temperature of the liquid • The movement of air above the surface • The nature of the liquid • Humidity – amount of water vapour in the atmosphere Stress and Strain Tension – forces act outwards in opposite directions and tend to lengthen the body. Compression – forces act inwards in opposite directions and tend to shorten the body. Shear – forces act in opposite directions along parallel faces, producing a tendency for parallel sections of the body to slide.

Torsion – a type of shearing which twists the body lengthwise. Stress – Force applied per unit cross-sectional area. Strain – extension per unit original length Young Modulus – ratio of stress to strain Hooke’s Law – states that force is proportional to the extension. Elastic Deformation – the material returns to original shape (length) once the applied force is removed. Plastic Deformation – the material does not return to its original shape (length) once the applied force is removed and is permanently deformed. Ultimate Tensile Stress – is the maximum stress that can be applied to a material before it breaks. Hysteresis – the stress-strain graph for loading is different from that for unloading. Energy is absorbed in a loading / unloading cycle. Creep – describes the very slow change in length or shape of certain metals even when the applied stress does not change. – Effect seems to depend on temperature. Fatigue - describes the fracture which sometimes occurs in metal samples after they have been subjected to a very large number of stress cycles. Waves There are two types of waves: 1) Progressive/Travelling -waves which moves energy from place to place -They allow transfer of energy -consists of a disturbance moving from a source to surrounding places as a result of which energy is transferred from one place to another. 2) – There •

Stationary / Standing do not travel along the medium are two types of stationary waves: Mechanical waves –produced by a disturbance (e.g. a vibrating body) in a material medium and are transmitted by the particles of the medium oscillating to and fro. -can be seen or felt •

Electromagnetic waves –are oscillating of electric and magnetic fields in space (no medium is required)

Two types of waves differ by how it travels:

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Transverse waves – waves where the particle movement is at right angles to the direction of propagation of waves. -have crests and troughs Longitudinal waves – are waves where the particle movement is parallel (in the same direction) to the propagation of waves. -have compressions and rarefactions.

Amplitude – magnitude of the maximum value of the displacement if the particle from its rest position. Wavelength – the smallest distance between two points which are in phase with each other. Period – is the time taken for one complete oscillation. Frequency - number of cycles passing a point per unit time of the source on the wave or of the point of the wave. Wave front - a line showing the position of the crest s of a wave – A line or surface on which the disturbance is in phase at all points. Phase difference – is a measure of a fraction of a cycle (or an oscillation) a particular point or wave is ahead or behind another point. Coherence – constant phase difference between the two waves. Wave speed – distance travelled per second by its wave crests. Polarisation – a wave property possessed only by transverse waves by which they are made to vibrate in a particular place. Polariser - a piece of transparent material (e.g. Polaroid) or device which will only allow the vibrations in a certain plane to pass through. Why transverse waves are only possible to be polarised: -Vibration in all possible directions -Longitudinal however, vibration is in direction of wave travel. •

Conditions : vibrations are in one plane only which contains the direction in which the wave is travelling

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Purpose: single direction of oscillation

• Application : -Reduces glare from reflecting surfaces -Stress analysis -Poor TV reception Diffraction – bending of waves or spreading of waves as it passes through an aperture or at an edge.

Principle of Superposition – When two or more waves meet at the same place at the same time the resultant displacement is equal to the vector sum of the individual displacements of the waves at that point. Uses of Superposition – 1) Fibre optics 2) Musical notes 1) Interference and diffraction pattern Interference – when two or more coherent waves (having a constant phase relationship) in the same region of space overlap, there is a change in overall intensity or displacement. Constructive interference – at some points, when the waves are in phase with each other, the resultant wave is of greater amplitude than any of its constituents. Destructive Interference – at some points, when the waves are completely out of phase with each other, the resultant wave cancels out. For observable interference pattern: -both waves must be of the same type -waves must meet at a point -both wave sources must be close enough -both waves are polarised in the same plane -both waves must be coherent -the amplitude of two waves must be roughly the same Otherwise: -completely dark fringe will never be obtained -the contrast pattern is reduced Conditions for constructive and Destructive patterns: 1) For Bright Fringes -path difference must be the whole number of wavelengths i.e. nλ

2) For Dark Fringes 2n+12λ

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Stationary waves – formed when two progressive waves of the same speed, amplitude and frequency travelling (in the same medium) in opposite directions meet.

Nodes – position of destructive interference – Where the amplitude is zero Antinodes – position of constructive interference – Amplitude of vibration is maximum End correction – at an open end of a column, the antinodes are slightly above the end of the tube.