1. 1
   A family owns an old set of Christmas tree lights in which all the small bulbs are connected in series, and they compare it with a newer set in which the bulbs are connected in parallel.

   (a)

   When one bulb fails, the whole string of lights goes out. Why does this happen in a series circuit?

   [1 mark]

   • ABecause the current is the same at every point in a series circuit, so breaking the circuit at one bulb stops current everywhere
   • BBecause the voltage is the same across every bulb in a series circuit
   • CBecause series circuits automatically repair broken components
   • DBecause current only flows through the last bulb in a series circuit

   (b)

   The family's newer set of lights has all the bulbs connected in parallel instead. What is the main advantage of connecting the lamps in parallel rather than in series for this application?

   [1 mark]

   • AParallel circuits always use less electrical energy overall
   • BIf one lamp fails, the others continue to work normally
   • CParallel lamps cannot be switched on and off independently
   • DParallel circuits require only one wire instead of two

   (c)

   State how the current from the supply compares with the current in each individual branch in the parallel set of lights, and state how the potential difference across each bulb compares with the potential difference across the whole set.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A factory's emergency lighting system uses four identical backup cells, each with an e.m.f. of 6 V, connected in series, feeding two identical resistive lamp units connected in series with each other in the same circuit.

   (a)

   What is the combined e.m.f. of the four cells connected in series?

   [1 mark]

   • A6 V
   • B10 V
   • C1.5 V
   • D24 V

   (b)

   The two identical lamp units in the emergency circuit each have a resistance of 4 ohms and are connected in series with each other. What is their combined resistance?

   [1 mark]

   • A2 ohms
   • B4 ohms
   • C8 ohms
   • D16 ohms

   (c)

   State how the current in the first lamp unit compares with the current in the second lamp unit in this series circuit, and state how the total potential difference across both lamp units compares with the individual potential differences across each one.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in a physics lesson connects a 6 ohm resistor and a 3 ohm resistor first in series, and then in parallel, across the same battery, to compare the combined resistance in each case.

   (a)

   A student connects a 6 ohm resistor and a 3 ohm resistor first in series, and then in parallel, across the same battery. Calculate the combined resistance of the two resistors when connected in series, and calculate the combined resistance when connected in parallel.

   [3 marks]

   (b)

   Explain why the combined resistance of the two resistors in parallel is smaller than the resistance of either individual resistor by itself, and explain, using the idea of current entering and leaving a junction, why the total current from the battery in the parallel arrangement is larger than the current through either resistor alone.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In the early days of domestic electric lighting, some homes were wired with all the room's lamps connected in series, similar to old Christmas lights, while other homes used the parallel wiring that has since become the standard for household electrical installations.

   (a)

   Explain, using ideas about current, potential difference and combined resistance, the practical problems that would arise from wiring a whole house's lamps in series, and explain why modern parallel wiring largely avoids these problems.

   [6 marks]

   (b)

   An electrician is asked to add one extra lamp to an existing parallel lighting circuit in a house, and separately to add one extra lamp to a (now rare) old series lighting circuit in a heritage building. Explain, using ideas about combined resistance and the sharing of current and potential difference, what effect adding the extra lamp would have in each case on the brightness of the lamps already present in that circuit.

   [6 marks]

   Total for question 4: 12 marks

End of questions