AQA GCSE Combined Science: Trilogy · 6.2

Electricity

50 revision questions with answers for 6.2 Electricity in AQA GCSE Combined Science: Trilogy (spec 8464). 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 6.2.1.2
What is electric current?
Answer:
The rate of flow of electrical charge; in metal wires, moving electrons carry the charge.
Question 2 · Spec 6.2.1.2
State the charge-flow equation.
Answer:
Q = It; charge Q in coulombs, current I in amperes and time t in seconds.
Question 3 · Spec 6.2.1.2
A current of 0.40 A flows for 30 s. Find charge flow.
Answer:
Q = 0.40 × 30 = 12 C.
Question 4 · Spec 6.2.1.2
Why is a closed circuit needed for a sustained current?
Answer:
Charge needs a complete conducting path and a source of potential difference.
Question 5 · Spec 6.2.1.3
What does potential difference measure?
Answer:
Energy transferred per unit charge between two points; 1 volt means 1 joule per coulomb.
Question 6 · Spec 6.2.1.3
What is electrical resistance?
Answer:
How strongly a component opposes current; at fixed potential difference, higher resistance gives lower current.
Question 7 · Spec 6.2.1.3
State the relationship between potential difference, current and resistance.
Answer:
V = IR; potential difference in volts, current in amperes and resistance in ohms.
Question 8 · Spec 6.2.1.3
A resistor has 6.0 V across it and 0.20 A through it. Find resistance.
Answer:
R = V/I = 6.0 / 0.20 = 30 ohms.
Question 9 · Spec 6.2.1.3
How is an ammeter connected?
Answer:
In series with the component whose current is measured.
Question 10 · Spec 6.2.1.3
How is a voltmeter connected?
Answer:
In parallel across the component whose potential difference is measured.
Question 11 · Spec 6.2.1.1
How do the standard symbols for an ammeter, voltmeter and resistor differ?
Answer:
Ammeter: circle with A; voltmeter: circle with V; resistor: rectangle in the circuit line.
Question 12 · Spec 6.2.1.4
What is the I-V relationship for an ohmic conductor at constant temperature?
Answer:
Current is directly proportional to potential difference, giving a straight line through the origin.
Question 13 · Spec 6.2.1.4
Why does a filament lamp's resistance increase as current increases?
Answer:
The filament heats up, increasing resistance, so current rises less rapidly as potential difference increases.
Question 14 · Spec 6.2.1.4
Describe a diode's I-V behaviour.
Answer:
It allows appreciable current mainly in one direction; reverse-direction resistance is very high.
Question 15 · Spec 6.2.1.4
How does a thermistor's resistance usually change when temperature rises?
Answer:
Its resistance decreases for the thermistors used in this specification.
Question 16 · Spec 6.2.1.4
How does an LDR's resistance change when light intensity rises?
Answer:
Its resistance decreases.
Question 17 · Spec 6.2.1.3 · Required practical
How can wire length's effect on resistance be investigated?
Answer:
Measure V and I for different lengths of the same wire; calculate R = V/I while keeping temperature and wire thickness constant.
Question 18 · Spec 6.2.1.3 · Required practical
Why use a small current and switch off between wire measurements?
Answer:
To limit heating, which would change resistance and confuse the effect of length.
Question 19 · Spec 6.2.1.3 · Required practical
What resistor combinations are included in the resistance required practical?
Answer:
Resistors in series and in parallel, comparing their current, potential difference and total resistance.
Question 20 · Spec 6.2.1.4 · Required practical
How are I-V characteristics measured?
Answer:
Vary potential difference, recording current and voltage across the component; plot current against voltage.
Question 21 · Spec 6.2.1.4 · Required practical
Why reverse the supply connections during an I-V investigation?
Answer:
To obtain readings for negative potential difference and current, showing the component's behaviour in both directions.
Question 22 · Spec 6.2.2
How does current behave in a series circuit?
Answer:
It is the same through every component.
Question 23 · Spec 6.2.2
How is supply potential difference shared in a series circuit?
Answer:
The potential differences across components add to the supply potential difference.
Question 24 · Spec 6.2.2
How is total resistance found for series resistors?
Answer:
Add the individual resistances: Rtotal = R₁ + R₂ + ...
Question 25 · Spec 6.2.2
Find current through 4-ohm and 8-ohm resistors in series across 6 V.
Answer:
Total resistance = 12 ohms; I = 6 / 12 = 0.50 A.
Question 26 · Spec 6.2.2
How does potential difference behave across parallel branches?
Answer:
Each branch has the same potential difference as the supply.
Question 27 · Spec 6.2.2
How do currents combine at a parallel junction?
Answer:
The total current entering equals the total leaving; supply current is the sum of branch currents.
Question 28 · Spec 6.2.2
What happens to total resistance when another parallel branch is added?
Answer:
It decreases because there is an additional route for charge flow.
Question 29 · Spec 6.2.2
Parallel branch currents are 0.30 A and 0.45 A. Find supply current.
Answer:
Total current = 0.30 + 0.45 = 0.75 A.
Question 30 · Spec 6.2.2
Why do adding series resistors and adding parallel resistors affect supply current differently?
Answer:
Series additions increase total resistance; parallel additions decrease it. At fixed supply voltage, current changes in the opposite direction.
Question 31 · Spec 6.2.3.1
What is alternating current?
Answer:
Current whose direction repeatedly reverses, produced by an alternating potential difference.
Question 32 · Spec 6.2.3.1
What is direct current?
Answer:
Current that flows in one direction, as supplied by a cell or battery.
Question 33 · Spec 6.2.3.1
What are the approximate UK mains potential difference and frequency?
Answer:
230 V and 50 Hz.
Question 34 · Spec 6.2.3.2
State the colours of live, neutral and earth insulation.
Answer:
Live: brown. Neutral: blue. Earth: green and yellow stripes.
Question 35 · Spec 6.2.3.2
What does the live wire do?
Answer:
It carries the alternating potential difference from the supply, about 230 V relative to earth.
Question 36 · Spec 6.2.3.2
What does the neutral wire do?
Answer:
It completes the circuit and is at or close to earth potential, about 0 V.
Question 37 · Spec 6.2.3.2
What is the earth wire's purpose?
Answer:
It is a safety connection at 0 V that can carry current during a fault, helping prevent an appliance's metal case remaining live.
Question 38 · Spec 6.2.3.2
Why can a live wire be dangerous even when a switch is open?
Answer:
It may still be connected to the supply; touching it while connected to earth can allow current through the body.
Question 39 · Spec 6.2.3.2
Why is a connection between live and earth hazardous?
Answer:
A large potential difference can drive current through the connection, including through a person.
Question 40 · Spec 6.2.4.1
State the power equation using potential difference and current.
Answer:
P = VI; power in watts, potential difference in volts and current in amperes.
Question 41 · Spec 6.2.4.1
A device takes 2.0 A at 12 V. Calculate its power.
Answer:
P = 12 × 2.0 = 24 W.
Question 42 · Spec 6.2.4.1
State the power equation using current and resistance.
Answer:
P = I²R.
Question 43 · Spec 6.2.4.1
Find power in a 5.0-ohm resistor carrying 2.0 A.
Answer:
P = 2.0² × 5.0 = 20 W.
Question 44 · Spec 6.2.4.2
State the equation connecting electrical energy, power and time.
Answer:
E = Pt; energy in joules, power in watts and time in seconds.
Question 45 · Spec 6.2.4.2
A 2,000 W kettle operates for 90 s. Find transferred energy.
Answer:
E = 2,000 × 90 = 180,000 J = 180 kJ.
Question 46 · Spec 6.2.4.2
State the equation connecting electrical energy, charge and potential difference.
Answer:
E = QV; energy in joules, charge in coulombs and potential difference in volts.
Question 47 · Spec 6.2.4.2
How much energy is transferred by 30 C crossing a 6.0 V component?
Answer:
E = 30 × 6.0 = 180 J.
Question 48 · Spec 6.2.4.2
How does an electric motor differ from a heater in useful output?
Answer:
A motor transfers energy mechanically; a heater transfers energy usefully to thermal stores.
Question 49 · Spec 6.2.4.3
What is the National Grid, and what do its transformers do?
Answer:
Cables and transformers connect power stations to consumers. Step-up transformers raise transmission voltage; step-down transformers lower it for users.
Question 50 · Spec 6.2.4.3
Why does high transmission voltage reduce wasted energy in cables?
Answer:
For a given power it lowers current, reducing heating losses because cable power loss is I²R.

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