In this experiment, you will investigate the absorption of thermal radiation by different coloured surfaces. You are provided with: • a lamp connected to a power supply • a thermometer with a piece of white card attached to its bulb • a thermometer with a piece of black card attached to its bulb • a clamp, boss and stand • a stopwatch • a 30 cm ruler. The supervisor has arranged the thermometer which has a piece of white card attached to its bulb so that the bulb is level with the filament of a lamp. The lamp is switched off. [Figure 2.1]

1. (a)(i)Record, in Table 2.1, the initial temperature θw shown on the thermometer.[1]
2. (a)(ii)Switch on the lamp, and at the same time, start the stopwatch. Record, in Table 2.1, the reading on the thermometer every 60s for 300 s. Switch off the lamp.[2]
3. (b)Carefully remove the thermometer from the clamp and place it on the bench. Place the thermometer which has a piece of black card attached to its bulb in the clamp. Make sure that the black card is facing the lamp and that the bulb of the thermometer is level with the filament of the lamp. Adjust the distance d between the lamp and the black card so that it is approximately 1 cm. Repeat the procedure in (a)(i) and (a)(ii) and record, in Table 2.1, the temperatures θb for the black card.[1]
4. (c)(i)Determine the temperature increase Δθ between t = 0 and t = 300s for each card. Δθ for white card = ..................................................... °C Δθ for black card = ..................................................... °C[1]
5. (c)(ii)Calculate the average rate of increase of temperature of each card. Use the equation: average rate of temperature increase = Δθ / t where t = 300 s. Include the unit in your answers. average rate of temperature increase of white card = ..................................................... unit average rate of temperature increase of black card = ..................................................... unit[2]
6. (d)Use your answers to (c)(ii) to deduce a conclusion which compares the absorption of thermal radiation by the two different coloured cards. State your conclusion.[1]
7. (e)State two variables that should be controlled in this experiment to ensure a valid conclusion. controlled variable 1 controlled variable 2[2]

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