The student changes the separation $d$ between the card attached to the thermometer bulb and the lamp until it is about 1 cm, then writes the initial thermometer temperature $\theta_W$ in Table 2.1. The thermometer appears in Fig. 2.2. Enter $\theta_W$ in Table 2.1 at $t=0$.
The student turns on the lamp and starts the stop-watch at the same moment, writes down the thermometer reading in Table 2.1 every 60 s for 5 minutes, and then turns the lamp off. Finish Table 2.1 by completing the time column.
The student takes the thermometer out of the clamp, puts in a thermometer with a black card fixed to its bulb, and repeats the method in (a). Find the temperature rise $\Delta\theta$ between $t=0$ and $t=300\,\text{s}$ for each card.
Calculate the rate of increase of temperature for each card. Use the equation rate of temperature increase $=\frac{\Delta\theta}{t}$. Make sure you include the unit.
Use your answers to (b)(ii) to reach a conclusion comparing the thermal-radiation absorption of the two cards. State your conclusion.
A student suggests that the rate of temperature increase is larger at the start of the experiment than at the end. State whether the results for the black card support this suggestion. Justify your answer by referring to the results.
State two variables that are kept the same in this experiment so that the comparison between the absorbing properties of white and black surfaces is valid.