4. Electricity and magnetism
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4.1 Simple phenomena of magnetism
4.1.1Forces between magnetic poles and
• Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised
4.1.2Induced magnetism
• Describe induced magnetism
4.1.3Differences between the properties of
• State the differences between the properties of temporary magnets (made of soft iron) and the properties of permanent magnets (made of steel
4.1.4Difference between magnetic and
• State the difference between magnetic and non-magnetic materials
4.1.5Magnetic field as a region in which a
• Describe a magnetic field as a region in which a magnetic pole experiences a force
4.1.6Pattern and direction of magnetic
• Draw the pattern and direction of magnetic field lines around a bar magnet
4.1.7Direction of a magnetic field at a
• State: the direction of a magnetic field at a point is the direction of the force on the N pole of a magnet at that point
4.1.8Plotting of magnetic field lines with
• Describe the plotting of magnetic field lines with a compass or iron filings and the use of a compass to determine the direction of the magnetic field
4.1.9Uses of permanent magnets and
• Describe the uses of permanent magnets and electromagnets
4.1.10Magnetic forces are due to
• Explain that magnetic forces are due to interactions between magnetic fields
4.1.11Relative strength of a magnetic field
• Know: the relative strength of a magnetic field is represented by the spacing of the magnetic field lines
4.2.1 Electric charge
4.2.1.1There are positive and negative
• State: there are positive and negative charges
4.2.1.2Positive charges repel other positive
• State: positive charges repel other positive charges, negative charges repel other negative charges, but positive charges attract negative charges
4.2.1.3Simple experiments to show the
• Describe simple experiments to show the production of electrostatic charges by friction and to show the detection of electrostatic charges
4.2.1.4Charging of solids by friction
• Explain that charging of solids by friction involves only a transfer of negative charge (electrons)
4.2.1.5An experiment to distinguish between
• Describe an experiment to distinguish between electrical conductors and insulators
4.2.1.6A simple electron model to explain the
• Recall/use a simple electron model to explain the difference between electrical conductors and insulators and give typical examples
4.2.1.7Charge is measured in coulombs
• State: charge is measured in coulombs
4.2.1.8An electric field as a region in which
• Describe an electric field as a region in which an electric charge experiences a force
4.2.1.9Direction of an electric field at a
• State: the direction of an electric field at a point is the direction of the force on a positive charge at that point
4.2.1.10Simple electric field patterns
• Describe simple electric field patterns, including the direction of the field: (a) around a point charge (b) around a charged conducting sphere (c) between two oppositely charged parallel conducting plates (end effects will not be examined)
4.2.2 Electric current
4.2.2.1Electric current is related to the
• Know: electric current is related to the flow of charge
4.2.2.2Use of ammeters (analogue and digital)
• Describe the use of ammeters (analogue and digital) with different ranges
4.2.2.3Electrical conduction in metals in
• Describe electrical conduction in metals in terms of the movement of free electrons
4.2.2.4Difference between direct current
• Know the difference between direct current (d.c.) and alternating current (a.c.)
4.2.2.5Electric current as charge passing a
• Define electric current as charge passing a point per unit time; recall/use: I = Q/t
4.2.2.6Conventional current is from positive
• State: conventional current is from positive to negative and that the flow of free electrons is from negative to positive
4.2.3 Electromotive force and potential difference
4.2.3.1Electromotive force (e.m.f.) as the
• Define electromotive force (e.m.f.) as the electrical work done by a source in moving a unit charge around a complete circuit
4.2.3.2E.m.f. is measured in volts (V)
• Know: e.m.f. is measured in volts (V)
4.2.3.3Potential difference (p.d.) as the
• Define potential difference (p.d.) as the work done by a unit charge passing through a component
4.2.3.4P.d. between two points is measured in
• Know: the p.d. between two points is measured in volts (V)
4.2.3.5Use of voltmeters (analogue and
• Describe the use of voltmeters (analogue and digital) with different ranges
4.2.3.6E.m.f.: E = W/Q
• Recall/use e.m.f.: E = W/Q
4.2.3.7P.d.: V = W/Q
• Recall/use p.d.: V = W/Q
4.2.4 Resistance
4.2.4.1Resistance: R = V/I
• Recall/use resistance: R = V/I
4.2.4.2An experiment to determine resistance
• Describe an experiment to determine resistance using a voltmeter and an ammeter and do the appropriate calculations
4.2.4.3State, qualitatively, the relationship
• State, qualitatively, the relationship of the resistance of a metallic wire to its length and to its cross-sectional area
4.2.4.4And explain the current–voltage graphs
• Sketch and explain the current–voltage graphs for a resistor of constant resistance, a filament lamp and a diode
4.2.4.5Following relationship for a metallic
• Recall/use the following relationship for a metallic electrical conductor: (a) resistance is directly proportional to length (b) resistance is inversely proportional to cross-sectional area
4.2.5 Electrical energy and electrical power
4.2.5.1Electric circuits transfer energy from
• Understand: electric circuits transfer energy from a source of electrical energy, such as an electrical cell or mains supply, to the circuit components and then into the surroundings
4.2.5.2Recall/use: for electrical power P =
• Recall/use: for electrical power P = IV
4.2.5.3Recall/use: for electrical energy E =
• Recall/use: for electrical energy E = IVt
4.2.5.4Kilowatt-hour (kWh) and calculate the
• Define the kilowatt-hour (kWh) and calculate the cost of using electrical appliances where the energy unit is the kWh
4.3.1 Circuit diagrams and circuit components
4.3.1.1Circuits with cells, batteries, power
• Draw/interpret circuits with cells, batteries, power supplies, generators, potential dividers, switches, resistors, heaters, thermistors (NTC), LDRs, lamps, motors, bells, ammeters, voltmeters, magnetising coils, transformers, fuses and relays; know each component behaviour
4.3.1.2Circuit diagrams containing diodes and
• Draw and interpret circuit diagrams containing diodes and light-emitting diodes (LEDs) and know how these components behave in the circuit
4.3.2 Series and parallel circuits
4.3.2.1Current at every point in a series
• Know: the current at every point in a series circuit is the same
4.3.2.2How to construct and use series and
• Know how to construct and use series and parallel circuits
4.3.2.3Combined e.m.f. of several sources in
• Calculate the combined e.m.f. of several sources in series
4.3.2.4Combined resistance of two or more
• Calculate the combined resistance of two or more resistors in series
4.3.2.5That, for a parallel circuit, the
• State that, for a parallel circuit, the current from the source is larger than the current in each branch
4.3.2.6Combined resistance of two resistors
• State: the combined resistance of two resistors in parallel is less than that of either resistor by itself
4.3.2.7Advantages of connecting lamps in
• State the advantages of connecting lamps in parallel in a lighting circuit
4.3.2.8Circuit rules: (a) current into a
• Recall/use circuit rules: (a) current into a junction equals current out (b) total p.d. across series components equals the sum of their p.d.s (c) p.d. across parallel branches is the same
4.3.2.9The sum of the currents into a
• Explain that the sum of the currents into a junction is the same as the sum of the currents out of the junction
4.3.2.10Combined resistance of two resistors
• Calculate the combined resistance of two resistors in parallel
4.3.3 Action and use of circuit components
4.3.3.1P.d. across an electrical conductor
• Know: the p.d. across an electrical conductor increases as its resistance increases for a constant current
4.3.3.2Action of a variable potential divider
• Describe the action of a variable potential divider
4.3.3.3Potential divider relation: R1/R2 =
• Recall/use potential divider relation: R1/R2 = V1/V2
4.4 Electrical safety
4.4.1Hazards of: (a) damaged insulation (b)
• State the hazards of: (a) damaged insulation (b) overheating cables (c) damp conditions (d) excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply
4.4.2A mains circuit consists of a live
• Know: a mains circuit consists of a live wire (line wire), a neutral wire and an earth wire and explain why a switch must be connected to the live wire for the circuit to be switched off safely
4.4.3Use and operation of trip switches and
• Explain the use and operation of trip switches and fuses and choose appropriate fuse ratings and trip switch settings
4.4.4Why the outer casing of an electrical
• Explain why the outer casing of an electrical appliance must be either non-conducting (double-insulated) or earthed
4.4.5A fuse without an earth wire protects
• State: a fuse without an earth wire protects the circuit and the cabling for a double- insulated appliance
4.5.1 Electromagnetic induction
4.5.1.1A conductor moving across a magnetic
• Know: a conductor moving across a magnetic field or a changing magnetic field linking with a conductor can induce an e.m.f. in the conductor
4.5.1.2An experiment to demonstrate EM
• Describe an experiment to demonstrate electromagnetic induction
4.5.1.3Factors affecting the magnitude of an
• State the factors affecting the magnitude of an induced e.m.f.
4.5.1.4Direction of an induced e.m.f. opposes
• Know: the direction of an induced e.m.f. opposes the change causing it
4.5.1.5And use the relative directions of
• State and use the relative directions of force, field and induced current
4.5.2 The a.c. generator
4.5.2.1Simple form of a.c. generator
• Describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip rings and brushes where needed
4.5.2.2And interpret graphs of e.m.f. against
• Sketch and interpret graphs of e.m.f. against time for simple a.c. generators and relate the position of the generator coil to the peaks, troughs and zeros of the e.m.f.
4.5.3 Magnetic effect of a current
4.5.3.1Pattern and direction of the magnetic
• Describe the pattern and direction of the magnetic field due to currents in straight wires and in solenoids
4.5.3.2An experiment to identify the pattern
• Describe an experiment to identify the pattern of the magnetic field (including direction) due to currents in straight wires and in solenoids
4.5.3.3Magnetic effect of a current is used
• Describe how the magnetic effect of a current is used in relays and loudspeakers and give examples of their application
4.5.3.4Qualitative variation of the strength
• State the qualitative variation of the strength of the magnetic field around straight wires and solenoids
4.5.3.5Effect on the magnetic field around
• Describe the effect on the magnetic field around straight wires and solenoids of changing the magnitude and direction of the current
4.5.4 Force on a current-carrying conductor
4.5.4.1An experiment to show that a force
• Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing: (a) the current (b) the direction of the field
4.5.4.2Relative directions of force, magnetic
• Recall/use the relative directions of force, magnetic field and current
4.5.4.3Direction of the force on beams of
• Determine the direction of the force on beams of charged particles in a magnetic field
4.5.5 The d.c. motor
4.5.5.1A current-carrying coil in a magnetic
• Know: a current-carrying coil in a magnetic field may experience a turning effect and that the turning effect is increased by increasing: (a) the number of turns on the coil (b) the current (c) the strength of the magnetic field
4.5.5.2Operation of an electric motor
• Describe the operation of an electric motor, including the action of a split-ring commutator and brushes
4.5.6 The transformer
4.5.6.1Construction of a simple transformer
• Describe the construction of a simple transformer with a soft-iron core, as used for voltage transformations
4.5.6.2Terms primary, secondary, step-up and
• Use the terms primary, secondary, step-up and step-down
4.5.6.3Transformer relation: Vp/Vs = Np/Ns
• Recall/use transformer relation: Vp/Vs = Np/Ns, where p and s mean primary and secondary
4.5.6.4Use of transformers in high- voltage
• Describe the use of transformers in high- voltage transmission of electricity
4.5.6.5Advantages of high-voltage
• State the advantages of high-voltage transmission
4.5.6.6Principle of operation of a simple
• Explain the principle of operation of a simple iron-cored transformer
4.5.6.7100% transformer efficiency: IpVp =
• Recall/use 100% transformer efficiency: IpVp = IsVs, where p and s mean primary and secondary
4.5.6.8Recall/use: P = I2R to explain why
• Recall/use: P = I2R to explain why power losses in cables are smaller when the voltage is greater