Section 4 - Electricity and Magnetism - With Notes Page

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

Electricity and Magnetism PAL (IGCSE) Single Science Revision Book - Section 4

Name:

_________________________________

Teacher:

_________________________________

DIPONT Educational Resource – Science

1

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

Syllabus Content_______________________________

DIPONT Educational Resource – Science

2

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

3

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

4

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

5

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

6

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

7

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

Syllabus Details________________________________ 4. Electricity and magnetism 4.1 Simple phenomena of magnetism Core • State the properties of magnets

• Give an account of induced magnetism INDUCED MAGNETISM:

If a piece of iron is brought close to a magnet it becomes magnetic and is attracted to the magnet.

• Distinguish between ferrous and non-ferrous materials FERROUS: NON-FERROUS:

Containing a large proportion of Iron (e.g. Iron, steel) Containing no iron

• Describe methods of magnetization and of demagnetization MAGNETISATION: Stroking a magnet across a material (e.g. iron) DEMAGNETISATION: Hitting the material • Describe an experiment to identify the pattern of field lines round a bar magnet

DIPONT Educational Resource – Science

8

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

9

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

10

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Distinguish between the magnetic properties of iron and steel

Material

Type

Properties

Iron Steel

Soft magnetic material Hard magnetic material

Magnetism is temporary Magnetism is permanent

• Distinguish between the design and use of permanent magnets and electromagnets

Type of magnet

Design

Use

Permanent

Hard magnetic material

Electromagnet

Uses a solenoid to create magnetic field

For applications where magnetism is needed over long periods – fridge doors For applications where the magnetic field needs to be turned on and off – Scrap metal moving

4.2 Electrical quantities 4.2 (a) Electric charge Core • Describe simple experiments to show the production and detection of electrostatic charges

DIPONT Educational Resource – Science

11

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

12

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

GOLD LEAF ELECTROSCOPE 

If a charge is moved close to the cap the gold leaf rises

• State that there are positive and negative charges There are two type of charges; POSITIVE and NEGATIVE • State that unlike charges attract and that like charges repel LIKE CHARGES UNLIKE CHARGES

– Repel - Attract

• Describe an electric field as a region in which an electric charge experiences a force

• Distinguish between electrical conductors and insulators and give typical examples ELECTRICAL CONDUCTOR: (metals)

DIPONT Educational Resource – Science

Charges are able to flow through the material

13

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism ELECTRICAL INSULATOR: Charges are unable to flow through the material (plastics)

DIPONT Educational Resource – Science

14

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

15

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism Supplement • State that charge is measured in coulombs Charge (Q) is measured in coulombs [C] • State the direction of lines of force and describe simple field patterns, including the field around a point charge and the field between two parallel plates

• Give an account of charging by induction

 

Charged rod brought close to top of electroscope The positive rod attracts electrons to the top of the electroscope (induced charge)

DIPONT Educational Resource – Science

16

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

17

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Recall and use the simple electron model to distinguish between conductors and insulators

 

In a conductor the charges are free to move (the electrons in a metal) In an insulator the charges are not free to move

4.2 (b) Current Core • State that current is related to the flow of charge CURRENT: Related to the flow of charge • Use and describe the use of an ammeter

DIPONT Educational Resource – Science

18

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

19

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism Supplement • Show understanding that a current is a rate of flow of charge and recall and use the equation I = Q /t

• Distinguish between the direction of flow of electrons and conventional current

4.2 (c) Electro-motive force Core • State that the e.m.f. of a source of electrical energy is measured in volts EMF is measured in Volts [V] Supplement • Show understanding that e.m.f. is defined in terms of energy supplied by a source in driving charge round a complete circuit

Electromotive force (e.m.f.): The total energy difference per unit charge around a circuit

4.2 (d) Potential difference Core • State that the potential difference across a circuit component is measured in volts Potential difference (pd) is measured in Volt [V]

DIPONT Educational Resource – Science

20

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

21

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Use and describe the use of a voltmeter

4.2 (e) Resistance Core • State that resistance = p.d./current and understand qualitatively how changes in p.d. or resistance affect current

• Recall and use the equation R = V/I

DIPONT Educational Resource – Science

22

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

23

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

24

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe an experiment to determine resistance using a voltmeter and an ammeter

• Relate (without calculation) the resistance of a wire to its length and to its diameter Supplement • Recall and use quantitatively the proportionality between resistance and length, and the inverse proportionality between resistance and cross-sectional area of a wire

R = Resistance  = Resistivity of material L = Length of conductor A = Area Summary  

Increasing length = increasing resistance Increasing cross-sectional area = decreasing resistance

DIPONT Educational Resource – Science

25

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

26

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.2 (f) Electrical energy Supplement • Recall and use the equations P =IV and E = IVt

4.3 Electric circuits 4.3 (a) Circuit diagrams Core • Draw and interpret circuit diagrams containing sources, switches, resistors (fixed and variable), lamps, ammeters, voltmeters, magnetizing coils, transformers, bells, fuses and relays

Supplement • Draw and interpret circuit diagrams containing diodes and transistors

DIPONT Educational Resource – Science

27

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

28

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

29

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.3 (b) Series and parallel circuits Core • Understand that the current at every point in a series circuit is the same

• Give the combined resistance of two or more resistors in series

• State that, for a parallel circuit, the current from the source is larger than the current in each branch

DIPONT Educational Resource – Science

30

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

31

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • State that the combined resistance of two resistors in parallel is less than that of either resistor by itself

• State the advantages of connecting lamps in parallel in a lighting circuit Parallel Circuit advantage: If one lamp fails the other lamps in parallel continue to function Supplement • Recall and use the fact that the sum of the p.d.s across the components in a series circuit is equal to the total p.d. across the supply

DIPONT Educational Resource – Science

32

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

33

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Recall and use the fact that the current from the source is the sum of the currents in the separate branches of a parallel circuit • Calculate the effective resistance of two resistors in parallel

4.3 (c) Action and use of circuit components Core • Describe the action of a variable potential divider (potentiometer)

 

The output voltage can be varied by changing the position of the potential divider The voltage dropped across that section of the resistor will vary

DIPONT Educational Resource – Science

34

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

35

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe the action of thermistors and light dependent resistors and show understanding of their use as input transducers

DIPONT Educational Resource – Science

36

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

37

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe the action of a capacitor as an energy store and show understanding of its use in time delay circuits

DIPONT Educational Resource – Science

38

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

39

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe the action of a relay and show understanding of its use in switching circuits

Supplement • Describe the action of a diode and show understanding of its use as a rectifier

A diode allows current to flow in only one one direction

DIPONT Educational Resource – Science

40

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

41

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

42

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe the action of a transistor as an electrically operated switch and show understanding of its use in switching circuits

• Recognise and show understanding of circuits operating as light sensitive switches and temperature-operated alarms (using a relay or a transistor)

DIPONT Educational Resource – Science

43

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

44

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.3 (d) Digital electronics Supplement • Explain and use the terms digital and analogue

• State that logic gates are circuits containing transistors and other components LOGIC GATES: Circuits containing transistors and other components • Describe the action of NOT, AND, OR, NAND and NOR gates • State and use the symbols for logic gates (candidates should use the American ANSI#Y 32.14 symbols)

DIPONT Educational Resource – Science

45

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

46

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Design and understand simple digital circuits combining several logic gates

4.4 Dangers of electricity Core • state the hazards of – damaged insulation DAMAGED INSULATION – risk of electrocution when handling wires etc – overheating of cables OVERHEATING OF CABLES – insulation will melt and wires become exposed – damp conditions DAMP CONDITIONS – impure water conducts electricity and so risk of electrocution • Show an understanding of the use of fuses and circuit-breakers FUSE:

A thin piece of wire which melts and breaks if too much current passes through it. Used to cut a circuit if the current is too high.

CIRCUIT BREAKER: Automatic electrical switch which will cut a circuit if the current is too high

DIPONT Educational Resource – Science

47

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

48

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.5 Electromagnetic effects 4.5 (a) Electromagnetic induction Core • Describe an experiment that shows that a changing magnetic field can induce an e.m.f. in a circuit • Show understanding that the direction of an induced e.m.f. opposes the change causing it

 

As the magnet is moved in and out of the coil the magnetic field in the coil changes The direction of the induced EMF and so current opposes the change causing it (i.e. makes a magnetic field opposite to the field of the moving magnet

Supplement • State the factors affecting the magnitude of an induced e.m.f. FACTORS EFFECTING MAGNITUDE OF INDUCED E.M.F. Increasing strength of magnet = increased induced E.M.F. Increasing velocity of motion of magnet = increased induced E.M.F. Increasing # of coils in solenoid = increased induced E.M.F.

DIPONT Educational Resource – Science

49

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

50

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.5 (b) a.c. generator Core • Describe a rotating-coil generator and the use of slip rings

AC GENERATOR   



If a coil is rotated in a permanent magnetic field the coil experiences a changing magnetic field If a wire experiences a changing magnetic field an EMF is induced If the wire is connected into a circuit a current will flow The slip rings allow the current to flow around a complete circuit as the coil rotates

• Sketch a graph of voltage output against time for a simple a.c. generator

DIPONT Educational Resource – Science

51

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

52

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.5 (c) Transformer Core • Describe the construction of a basic iron-cored transformer as used for voltage transformations • Recall and use the equation (Vp /Vs) = (Np /Ns) Supplement • Describe the principle of operation of a transformer • Recall and use the equation Vp Ip = Vs Is (for 100% efficiency)

for 100% efficiency THE TRANSFORMER…     

An AC current is passed through the primary coil A varying magnetic field is induced in the coil and the iron core The secondary coil experiences a varying magnetic field An EMF and so current is induced in the secondary coil The output current is also alternating

DIPONT Educational Resource – Science

53

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

54

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe the use of the transformer in high voltage transmission of electricity

TRANSFORMERS ARE USED IN ELECTRICTY TRANSMISSION BECAUSE...   

The output of a power station is high current The transformer is used to convert this to low current and high voltage before passing through the overhead cables A second transformer is used to lower the current and voltage before the supply enters homes

• Give the advantages of high-voltage transmission HIGH VOLTAGE TRANSMISSION = Low energy losses through heating in the cables • Explain why energy losses in cables are lower when the voltage is high High voltage …. Low current …… Less heating of the cable …… Low energy loses

DIPONT Educational Resource – Science

55

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

56

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.5 (d) The magnetic effect of a current Core • Describe the pattern of the magnetic field due to currents in straight wires and in solenoids Supplement • State the qualitative variation of the strength of the magnetic field over salient parts of the pattern • Describe the effect on the magnetic field of changing the magnitude and direction of the current

GENERAL CONVENTION FOR MAGNETIC FIELD LINES...   

The arrow points towards the south pole The spacing of the field lines is proportional to the magnetic field strength If the current changes direction the magnetic field will reverse in direction

DIPONT Educational Resource – Science

57

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

58

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

59

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Describe applications of the magnetic effect of current, including the action of a relay

ACTION OF A RELAY…    

With no current through the coil there is no magnetic field in the coil The contacts will be separate When a current passes through the coil a magnetic field is induced The contacts will become magnetized and so close

4.5 (e) Force on a current-carrying conductor Core • Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing: (i) the current (ii) the direction of the field

DIPONT Educational Resource – Science

60

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism If the current is reversed – The force will act in the opposite direction If the field direction is reversed – The force will act in the opposite direction

DIPONT Educational Resource – Science

61

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

62

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism Supplement • State and use the relative directions of force, field and current

• Describe an experiment to show the corresponding force on beams of charged particles

When using the left hand rule for charged particles…  For electrons the direction of current is the opposite direction to the electron velocity  For protons the direction of current is the same direction as the electron velocity

DIPONT Educational Resource – Science

63

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

DIPONT Educational Resource – Science

64

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

65

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.5 (f) d.c. motor Core • State that a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing the number of turns on the coil • Relate this turning effect to the action of an electric motor Supplement • Describe the effect of increasing the current

THE ELECTRIC MOTOR    

A current is passed through a coil in a magnetic field If a current carrying wire is placed in a magnetic field it experiences a force The coil feels a force which rotates the coil The commutator ensures that the current flows around the coil to give a force which always acts to rotate the coil in the same direction

To Increase the rate of rotation...   

Increase the number of coils Increase the strength of the magnetic field Increase the current

DIPONT Educational Resource – Science

66

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

67

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

4.6 Cathode-ray oscilloscopes 4.6 (a) Cathode rays Core • Describe the production and detection of cathode rays

DETECTION OF CATHODE RAYS  

Cathode rays can be detected by a fluorescent screen When the rays are incident on the screen the screen emit’s light

• Describe their deflection in electric fields



Cathode rays are deflected towards the positive of an electric field

DIPONT Educational Resource – Science

68

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism 

This indicates that the cathode rays are negatively charged

DIPONT Educational Resource – Science

69

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

70

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • State that the particles emitted in thermionic emission are electrons The particles emitted in thermionic emission are electrons

4.6 (b) Simple treatment of cathode-ray oscilloscope Supplement • Describe (in outline) the basic structure and action of a cathode-ray oscilloscope (detailed circuits are not required)

 

Electrons are generated by the hot element The electrons are accelerated towards the anode and focused into a beam

DIPONT Educational Resource – Science

71

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism  

The deflection coils direct the beam at a certain position in the screen The fluorescent screen indicates the position of the beam

DIPONT Educational Resource – Science

72

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism

NOTES PAGE

DIPONT Educational Resource – Science

73

PAL (IGCSE) – PHYSICS Section 4 Electricity and Magnetism • Use and describe the use of a cathode-ray oscilloscope to display waveforms

KEY CONTROLS….  

Time base: Time taken for beam to pass through one horizontal division [Sec/div] Vertical amplifier gain: The vertical scale control [Volts/div]

DIPONT Educational Resource – Science

74