A non-contact monitoring system measures the thermal radiation emitted by railway wheel bearings.
The table shows calibration data for a bearing at four temperatures.
| Temperature in ∘C^{\circ}\text{C}∘C | Peak wavelength in μm\mu\text{m}μm | Total emitted intensity in W/m2\mathrm{W/m^2}W/m2 |
|---|---|---|
| 20 | 9.9 | 420 |
| 45 | 9.1 | 580 |
| 120 | 7.4 | 1350 |
| 300 | 5.1 | 6100 |
Detector P measures wavelengths from 4.0 μm4.0\ \mu\text{m}4.0 μm to 7.0 μm7.0\ \mu\text{m}7.0 μm.
Detector Q measures wavelengths from 7.0 μm7.0\ \mu\text{m}7.0 μm to 14.0 μm14.0\ \mu\text{m}14.0 μm.
The system records which detector measures the peak wavelength and also estimates the total emitted intensity. A normal bearing operates at 45 ∘C45\ ^{\circ}\text{C}45 ∘C. A severely overheating bearing can reach 300 ∘C300\ ^{\circ}\text{C}300 ∘C.
Use the data to explain how the monitoring system could identify a severely overheating bearing.
The severely overheating bearing becomes hotter than 300 ∘C300\ ^{\circ}\text{C}300 ∘C.
Predict two changes to its wavelength distribution.
An engineer says that the bearing at 300 ∘C300\ ^{\circ}\text{C}300 ∘C emits radiation only at a wavelength of 5.1 μm5.1\ \mu\text{m}5.1 μm.
Explain why the engineer is wrong.
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.