In this experiment, you will measure the efficiency of a small electric heater constructed from a coil of wire. You are provided with a circuit consisting of: • a power supply • a coil of wire in a beaker (the coil of wire is the heater) • an ammeter • a voltmeter • a switch in the open position • connecting wires. You are also provided with: • a thermometer • a stirrer • a supply of water at room temperature • a measuring cylinder • a stopwatch.

1. (a)In the answer space, draw a circuit diagram of the circuit that has been set up for you.[2]
2. (b)Use the measuring cylinder to measure 50 cm³ of water. Pour the water into the beaker containing the heater. Make sure that the water covers the heater. Measure and record the initial temperature 𝜃₀ of the water in the beaker. 𝜃₀ = ..................................................... °C[1]
3. (c)(i)Close the switch, and start the stopwatch immediately. Record the current I in the circuit and the potential difference V across the heater. I = ................................................................. A V = ................................................................. V[1]
4. (c)(ii)Leave the circuit switched on for 5 minutes. During this time, gently stir the water using the stirrer. After 5 minutes, open the switch. Continue to stir the water for a further minute before recording the temperature again. This is the final temperature 𝜃F. Record 𝜃F and calculate the temperature change Δθ. Use the equation shown. Δθ = 𝜃F – 𝜃₀ 𝜃F = ................................................................. °C Δθ = ................................................................. °C[1]
5. (c)(iii)Explain why the water is stirred for a further minute after the circuit is switched off.[1]
6. (d)(i)The energy Qᴴ supplied by the heater is given by Qᴴ = I x V x t where t = 300 s. Calculate Qᴴ. Show your working. Qᴴ = ................................................................. J[1]
7. (d)(ii)The energy Qw gained by the water is given by the equation shown. Qw = 50 × 4.2 × Δθ Calculate Qw. Show your working. Qw= ................................................................. J[1]
8. (d)(iii)The efficiency of the heater is given by the equation shown. efficiency = Qw / Qᴴ Calculate the efficiency of the heater. Show your working. efficiency = .................................................................[1]
9. (e)Suggest one change that can be made to the apparatus you have used in this investigation that will increase the efficiency of the heater.[1]