A metal sample holder is inside an evacuated chamber and exchanges energy with its surroundings only by radiation. It has a mass of 0.80 kg and a specific heat capacity of 500 J/kg ∘C500\ \text{J/kg}\ ^{\circ}\text{C}500 J/kg ∘C.
A radiation source is switched on. The average power absorbed by the holder remains at 92 W. The table gives the average power emitted during each time interval.
| time interval in s | average emitted power in W |
|---|---|
| 0 to 15 | 68 |
| 15 to 30 | 69 |
| 30 to 45 | 70 |
| 45 to 60 | 71 |
The emitted power of the holder at different temperatures is shown in the table.
| temperature in ∘C^{\circ}\text{C}∘C | emitted power in W |
|---|---|
| 20 | 68 |
| 30 | 78 |
| 40 | 89 |
| 50 | 102 |
Calculate the temperature rise of the holder during the first 60 s.
Use the equation
ΔQ=m×c×Δθ\Delta Q = m \times c \times \Delta \thetaΔQ=m×c×Δθ
The holder is at 30 ∘C30\ ^{\circ}\text{C}30 ∘C. A technician proposes keeping the absorbed power constant at 78 W to maintain this temperature. Evaluate this proposal.
96 exam-style questions on Edexcel GCSE Physics 5.3 Black body radiation, covering 5.3.1 Emission of radiation and temperature, 5.3.2 Radiation balance and constant temperature, and 5.3.3 The temperature of the Earth. Each one has a worked solution and a mark scheme showing where the marks go.