You will investigate the resistance of a lamp. You are provided with: • a power supply • a lamp • a switch in the 'off' position • an ammeter • a voltmeter. You are also provided with a 10Ω resistor and an additional connecting lead.

1. (a)The circuit shown in Fig. 1.1 has been set up for you. [Figure 1.1]
2. (a)(i)Close the switch. Record the readings of current Iₗ and potential difference Vₗ. Iₗ = _______ A Vₗ = _______ V Open the switch.[2]
3. (a)(ii)Suggest why you are instructed to open the switch after you have recorded the readings.[1]
4. (a)(iii)Use the equation: V R = --- I to calculate the resistance Rₗ of the lamp. Give your answer to 2 significant figures.[2]
5. (b)Disconnect the voltmeter at point P. Add the 10Ω resistor into the circuit in series with the lamp and reconnect the voltmeter as shown in Fig. 1.2. [Figure 1.2]
6. (b)(i)Repeat (a)(i) to find the readings of I𝒸 and V𝒸. Use the equation given in (a)(iii) to find the combined resistance R𝒸 of the lamp and the resistor connected in series. I𝒸 = _______ A V𝒸 = _______ V R𝒸 = _______ Ω[2]
7. (b)(ii)Theory states that the value of the resistance of the lamp Rₗ in the circuit shown in Fig. 1.2 is given by: Rₗ = R𝒸 – 10Ω Find the resistance of the lamp Rₗ predicted by theory. predicted Rₗ = _______ Ω[1]
8. (b)(iii)Use your values of the current in the circuits and any observations about the brightness of the lamp to explain why the value of Rₗ in (b)(ii) is lower than in (a)(iii).[2]

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