State — 4 marks
A student is designing a lighting system for a bedroom. They need to decide whether to wire two ceiling lights in series or in parallel. The student wants to understand the advantages and disadvantages of each arrangement.
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(a) State one advantage of connecting the two ceiling lights in parallel rather than in series.
[1 mark]
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(b) State what happens to the total resistance of the circuit when a third identical light is added in parallel with the first two lights.
[1 mark]
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(c) State two differences between a series circuit and a parallel circuit in terms of current flow.
[2 marks]
Show mark scheme
- (a) Each light can be switched on/off independently (or each light receives the full voltage/or if one light breaks the other still works)
- (b) The total resistance decreases (or gets smaller)
- (c) In series, current is the same at all points / In parallel, current splits at junctions (or current divides)
- (c) In series, there is only one path for current / In parallel, there are multiple paths for current
Calculate — 3 marks
A student designs a circuit for a model railway layout. She connects a 12 V power supply to a circuit containing three resistors. Two identical resistors of 6 Ω are connected in parallel with each other, and this combination is connected in series with a third resistor of 4 Ω.
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(a) Calculate the combined resistance of the two 6 Ω resistors connected in parallel.
[1 mark]
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(b) Calculate the total resistance of the circuit.
[1 mark]
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(c) Calculate the total current supplied by the 12 V power supply.
[1 mark]
Show mark scheme
- (a) Uses 1/R_total = 1/R₁ + 1/R₂ (or equivalent) to give 3 Ω (accept 3.0 Ω)
- (b) Adds series resistances: 3 + 4 = 7 Ω (accept 7.0 Ω)
- (c) Uses I = V/R to give 12/7 = 1.71 A (or 1.7 A) (accept answers in range 1.70–1.72 A)
Define — 4 marks
A student is designing a lighting system for a bedroom. They need to install multiple LED bulbs that can be controlled independently, and they want to ensure that if one bulb fails, the others continue to work. They are deciding between wiring the bulbs in series or in parallel.
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(a) Define what is meant by a parallel circuit.
[1 mark]
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(b) Define what is meant by the term 'potential difference' across a component in a circuit.
[1 mark]
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(c) Explain why a parallel circuit arrangement would be more suitable for the student's bedroom lighting system than a series circuit arrangement, using your knowledge of how components behave in each type of circuit.
[2 marks]
Show mark scheme
- (a) A circuit where components are connected on separate branches/pathways (1 mark)
- (b) The work done per unit charge (or energy transferred per unit charge) across the component (1 mark)
- (c) In a parallel circuit, if one bulb fails/breaks the circuit is not broken at that point, so other bulbs continue to work (1 mark)
- (c) In a series circuit, if one bulb fails, the entire circuit is broken and all bulbs stop working / each bulb has its own complete circuit path in parallel (1 mark)
Explain — 3 marks
A student is comparing two sets of lights in their home. An old set of Christmas tree lights stops working completely when a single bulb breaks. However, the recessed ceiling lights in their kitchen continue to work even when one of the bulbs has stopped working.
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(a) Explain why all the Christmas tree lights go out when one bulb breaks.
[1 mark]
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(b) Explain why the kitchen ceiling lights stay on when one bulb stops working.
[2 marks]
Show mark scheme
- (a) The bulbs are connected in series (so there is only one path for current) / if one bulb breaks the circuit is incomplete
- (b) The bulbs are connected in parallel (so there is more than one path for current)
- (b) Current can still flow through the other bulbs / the other bulbs still have a complete circuit
Describe — 2 marks
A student is setting up decorative lights for a school play. The student tests two different ways of connecting the lights. In one circuit, the lights are connected in series. In the other circuit, the lights are connected in parallel.
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(a) Describe what happens to the other bulbs in a series circuit when one bulb is removed.
[1 mark]
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(b) Describe one advantage of connecting decorative lights in parallel rather than in series.
[1 mark]
Show mark scheme
- (a) the other bulbs go out
- (a) the other bulbs stop working
- (a) the other bulbs switch off
- (b) if one bulb breaks the others stay on
- (b) the other bulbs keep working
- (b) each bulb can be switched on or off independently
- (b) the bulbs are brighter
GCSE Perfect