Electricity
50 exam-style questions with answers for 4.2 Electricity in AQA GCSE Physics (spec 8463). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below. Not official AQA material.
All 50 questions and answers
Question 1 · Spec 4.2.1.1 · Circuit symbols
Describe the circuit symbol for a diode. [1 mark]
Answer:A triangle pointing in the direction of current, with a line across its point, in a straight wire.Question 2 · Spec 4.2.1.1 · Circuit symbols
Name the component whose resistance decreases as light intensity increases. [1 mark]
Answer:A light-dependent resistor (LDR).Question 3 · Spec 4.2.1.2 · Current
Define electric current. [1 mark]
Answer:The rate of flow of electrical charge.Question 4 · Spec 4.2.1.2 · Charge
State the equation linking charge, current and time. [1 mark]
Answer:Charge flow = current × time (Q = It).Question 5 · Spec 4.2.1.2 · Charge
A current of 0.4 A flows for 2 minutes. Calculate the charge that flows. [2 marks]
Answer:Q = It = 0.4 × 120 (1); = 48 C (1).Question 6 · Spec 4.2.1.2 · Current
What is the current like at different points in a single closed loop? [1 mark]
Answer:It is the same at every point.Question 7 · Spec 4.2.1.3 · Resistance
State the equation linking potential difference, current and resistance. [1 mark]
Answer:Potential difference = current × resistance (V = IR).Question 8 · Spec 4.2.1.3 · Resistance
A 12 V supply drives a current of 0.5 A through a resistor. Calculate its resistance. [2 marks]
Answer:R = V ÷ I = 12 ÷ 0.5 (1); = 24 Ω (1).Question 9 · Spec 4.2.1.3 · Required practical 3
Describe how to investigate how the length of a wire affects its resistance. [3 marks]
Answer:Connect the wire in series with an ammeter and a power supply, with a voltmeter in parallel across the wire (1); measure V and I for different lengths using crocodile clips on a ruler (1); calculate R = V ÷ I for each length (1).Question 10 · Spec 4.2.1.3 · Required practical 3
Why should the current be kept low in the resistance practical? [1 mark]
Answer:To stop the wire heating up, which would increase its resistance.Question 11 · Spec 4.2.1.4 · Ohmic conductors
What is an ohmic conductor? [2 marks]
Answer:A conductor where current is directly proportional to potential difference (1); at constant temperature, so resistance stays constant (1).Question 12 · Spec 4.2.1.4 · Filament lamps
Explain the shape of the I–V graph for a filament lamp. [2 marks]
Answer:As current increases, the filament gets hotter (1); so its resistance increases and the graph curves (1).Question 13 · Spec 4.2.1.4 · Diodes
Describe the resistance of a diode. [2 marks]
Answer:Very low resistance in the forward direction (1); very high resistance in the reverse direction, so current flows only one way (1).Question 14 · Spec 4.2.1.4 · Thermistors
Describe how the resistance of a thermistor changes and give a use. [2 marks]
Answer:Its resistance decreases as temperature increases (1); used in thermostats or fire alarms (1).Question 15 · Spec 4.2.1.4 · LDRs
Give a use of an LDR. [1 mark]
Answer:Switching on street lights automatically when it gets dark.Question 16 · Spec 4.2.1.4 · Required practical 4
Why is the supply reversed when finding the I–V characteristic of a diode? [1 mark]
Answer:To show the behaviour in both directions; current only flows one way.Question 17 · Spec 4.2.2 · Series circuits
State three rules for series circuits. [3 marks]
Answer:The same current flows through each component (1); the total potential difference is shared between components (1); total resistance is the sum of the resistances (1).Question 18 · Spec 4.2.2 · Parallel circuits
State two rules for parallel circuits. [2 marks]
Answer:The potential difference across each branch is the same (1); the total current is the sum of the currents in each branch (1).Question 19 · Spec 4.2.2 · Series circuits
A 4 Ω and a 6 Ω resistor are in series. Calculate the total resistance. [1 mark]
Answer:4 + 6 = 10 Ω.Question 20 · Spec 4.2.2 · Parallel circuits
Explain why adding resistors in parallel decreases total resistance. [2 marks]
Answer:Each extra branch gives another path for current (1); so the total current increases for the same potential difference (1).Question 21 · Spec 4.2.2 · Series circuits
A 9 V battery is connected to two resistors in series. The p.d. across one is 3.5 V. What is the p.d. across the other? [1 mark]
Answer:9 − 3.5 = 5.5 V.Question 22 · Spec 4.2.3.1 · a.c. and d.c.
What is the difference between direct and alternating potential difference? [2 marks]
Answer:Direct p.d. is in one direction only (1); alternating p.d. continuously changes direction (1).Question 23 · Spec 4.2.3.1 · Mains electricity
State the frequency and potential difference of UK mains electricity. [2 marks]
Answer:50 Hz (1); about 230 V (1).Question 24 · Spec 4.2.3.2 · Plugs
State the colour and function of the earth wire. [2 marks]
Answer:Green and yellow stripes (1); a safety wire to stop the appliance casing becoming live (1).Question 25 · Spec 4.2.3.2 · Plugs
State the colour of the live and neutral wires. [2 marks]
Answer:Live: brown (1); neutral: blue (1).Question 26 · Spec 4.2.3.2 · Plugs
Why can touching the live wire be dangerous even if a switch is off? [2 marks]
Answer:The live wire is at about 230 V, while your body is at 0 V (1); a large current may flow through you to earth, giving an electric shock (1).Question 27 · Spec 4.2.4.1 · Power
State two equations for electrical power. [2 marks]
Answer:P = VI (1); P = I²R (1).Question 28 · Spec 4.2.4.1 · Power
Calculate the power of a 230 V heater that draws 8 A. [2 marks]
Answer:P = VI = 230 × 8 (1); = 1840 W (1).Question 29 · Spec 4.2.4.1 · Power
A current of 2 A flows through a 50 Ω resistor. Calculate the power. [2 marks]
Answer:P = I²R = 2² × 50 (1); = 200 W (1).Question 30 · Spec 4.2.4.2 · Energy transfers
State the equation linking energy, charge and potential difference. [1 mark]
Answer:Energy transferred = charge flow × potential difference (E = QV).Question 31 · Spec 4.2.4.2 · Energy transfers
Calculate the energy transferred when 30 C flows through a p.d. of 12 V. [2 marks]
Answer:E = QV = 30 × 12 (1); = 360 J (1).Question 32 · Spec 4.2.4.2 · Energy transfers
A 1500 W hairdryer is used for 10 minutes. Calculate the energy transferred. [2 marks]
Answer:E = Pt = 1500 × 600 (1); = 900 000 J (1).Question 33 · Spec 4.2.4.2 · Appliances
Describe the energy transfer in an electric kettle. [2 marks]
Answer:Energy is transferred electrically from the mains (1); to the thermal energy store of the water (1).Question 34 · Spec 4.2.4.3 · National Grid
What is the National Grid? [1 mark]
Answer:A system of cables and transformers linking power stations to consumers.Question 35 · Spec 4.2.4.3 · National Grid
Why is electricity transmitted at a very high potential difference? [2 marks]
Answer:This gives a low current for the same power (1); so less energy is lost as heat in the cables, making it more efficient (1).Question 36 · Spec 4.2.4.3 · Transformers
What do step-up and step-down transformers do in the National Grid? [2 marks]
Answer:Step-up transformers increase the p.d. from power stations to the transmission cables (1); step-down transformers decrease it to a safe level for homes (1).Question 37 · Spec 4.2.5.1 · Static electricity
Explain how a balloon becomes charged when rubbed with a cloth. [2 marks]
Answer:Electrons are transferred from the cloth to the balloon by friction (1); the balloon gains electrons and becomes negatively charged (1).Question 38 · Spec 4.2.5.1 · Static electricity
What happens when two objects with the same charge are brought together? [1 mark]
Answer:They repel.Question 39 · Spec 4.2.5.1 · Static electricity
Why do sparks occur? [2 marks]
Answer:A large charge builds up, creating a high potential difference (1); electrons jump across the gap through the air (1).Question 40 · Spec 4.2.5.2 · Electric fields
Describe the electric field around a charged object. [2 marks]
Answer:A region where another charged object experiences a non-contact force (1); the field is stronger closer to the object (1).Question 41 · Spec 4.2.5.2 · Electric fields
In which direction do electric field lines point around a positive charge? [1 mark]
Answer:Outwards, away from the charge.Question 42 · Spec 4.2.1.3 · Resistance
Calculate the current through a 15 Ω resistor with a p.d. of 6 V. [2 marks]
Answer:I = V ÷ R = 6 ÷ 15 (1); = 0.4 A (1).Question 43 · Spec 4.2.1.2 · Current
How is an ammeter connected in a circuit? [1 mark]
Answer:In series with the component.Question 44 · Spec 4.2.1.2 · Potential difference
How is a voltmeter connected in a circuit? [1 mark]
Answer:In parallel across the component.Question 45 · Spec 4.2.2 · Parallel circuits
A parallel circuit has branch currents of 0.3 A and 0.5 A. What is the current from the supply? [1 mark]
Answer:0.3 + 0.5 = 0.8 A.Question 46 · Spec 4.2.3.2 · Fuses
How does a fuse protect an appliance? [2 marks]
Answer:If the current is too high, the fuse wire melts (1); breaking the circuit and stopping the current (1).Question 47 · Spec 4.2.4.2 · Appliances
Why are appliances given a power rating? [1 mark]
Answer:It shows the energy they transfer each second, so they can be compared.Question 48 · Spec 4.2.5.1 · Static electricity
Why does a charged comb attract small pieces of paper? [1 mark]
Answer:The charged comb induces an opposite charge on the near side of the paper, which is attracted.Question 49 · Spec 4.2.4.1 · Power
Calculate the current drawn by a 60 W lamp on a 230 V supply. [2 marks]
Answer:I = P ÷ V = 60 ÷ 230 (1); = 0.26 A (1).Question 50 · Spec 4.2.1.4 · Thermistors
A thermistor is at 20 °C and is then heated. What happens to the current through it if p.d. is constant? [1 mark]
Answer:The current increases, because its resistance decreases.