Physics
Electricity and magnetism — Topics 4-5
- 1.
Two resistors of 6.0 Ω and 3.0 Ω are connected in parallel. Calculate their combined resistance.
[3 marks] - 2.
An ideal transformer has 1200 turns on its primary coil and 80 turns on its secondary coil. The primary voltage is 240 V. Calculate the secondary voltage and state whether it is step-up or step-down.
[4 marks] - 3.
A current of 3.0 A flows through a resistor for 5 minutes. Calculate the charge that flows.
[3 marks] - 4.
A 12 V battery drives a current of 2.0 A through a resistor. Calculate the resistance and the power dissipated.
[4 marks] - 5.
State the difference between series and parallel circuits in terms of current at different points in the circuit.
[2 marks] · no calculator - 6.
A wire carries a current through a magnetic field. State the rule used to determine the direction of the force on the wire, and state the three quantities it relates.
[3 marks] · no calculator - 7.
Three 4.0 Ω resistors are connected in series with a 24 V battery. Calculate the current flowing and the voltage across each resistor.
[4 marks] - 8.
Explain why a fuse of appropriate rating is fitted in the live wire of a mains electrical appliance, in terms of safety.
[3 marks] · no calculator - 9.
Two 6.0 Ω resistors are connected in parallel, and this combination is connected in series with a 3.0 Ω resistor. Calculate the total resistance of the circuit.
[4 marks] - 10.
Explain how a step-up transformer is used to reduce energy losses during the transmission of electrical power over long distances on the national grid.
[4 marks] · no calculator - 11.
A graph of current against potential difference for a resistor kept at constant temperature is a straight line through the origin. State what this shows about the resistance of the resistor, and calculate its resistance if a current of 0.40 A flows when the potential difference is 6.0 V.
[3 marks] - 12.
State how the current through a diode depends on the direction of the applied potential difference, and name one application of a diode in a circuit.
[2 marks] · no calculator - 13.
Describe how the resistance of a filament lamp changes as the current through it increases, and explain why, in terms of temperature.
[3 marks] · no calculator - 14.
A light-dependent resistor (LDR) is used to automatically switch on a street light at night. State how the resistance of an LDR changes as light intensity decreases, and explain how this can be used to switch the light on in darkness.
[3 marks] · no calculator - 15.
A thermistor is used as part of a fire alarm circuit. State how the resistance of a thermistor changes as temperature increases, and explain how this allows the circuit to detect a fire.
[3 marks] · no calculator - 16.
A bar magnet is pushed into a coil of wire connected to a sensitive ammeter, inducing a current. State three factors that would increase the size of the induced current, and state how the direction of the induced current would change if the magnet were withdrawn instead of inserted.
[4 marks] · no calculator - 17.
Describe the basic construction of a simple d.c. electric motor, and state the purpose of the split-ring commutator.
[3 marks] · no calculator - 18.
State two factors that increase the strength of an electromagnet, and describe one practical application of an electromagnet.
[3 marks] · no calculator - 19.
A polythene rod is rubbed with a cloth and becomes negatively charged. Explain, in terms of electron transfer, why the rod becomes negatively charged, and state what type of charge the cloth acquires.
[3 marks] · no calculator - 20.
A 2.5 kW electric heater is used for 4.0 hours. Calculate the energy transferred in kilowatt-hours, and the cost of using the heater if electricity costs 18 cents per kWh.
[4 marks] - 21.
A charge of 5.0 C passes through a component when a potential difference of 12 V is maintained across it. Calculate the electrical energy transferred.
[3 marks] - 22.
Describe the behaviour of a two-input AND logic gate: state the condition needed for its output to be 1 (high), and state the output for all other combinations of inputs A and B.
[3 marks] · no calculator - 23.
Explain why a relay is used to allow a low-current circuit, such as one containing a sensor, to switch a separate high-current circuit, such as one containing a motor.
[3 marks] · no calculator - 24.
Describe the shape of the magnetic field pattern around a straight current-carrying wire, and state how the field pattern of a solenoid compares to that of a bar magnet.
[3 marks] · no calculator - 25.
Three identical 1.5 V cells are connected in series in a circuit. Calculate the total e.m.f. of the battery, and state how the total e.m.f. would differ if the same three cells were instead connected in parallel.
[3 marks]