An electric motor is enclosed by a metal casing. A cooler, temperature-sensitive cable is fixed beside the casing. Two casings are identical apart from their surface finish: one is matt black and the other is glossy white. During operation, each casing would be at the same temperature and in the same position relative to the cable. The engineer wants to reduce the energy transferred from the casing to the cable by infrared radiation.
Which casing should the engineer choose?
The matt black casing, because emitting infrared radiation makes the cable lose energy to the casing.
The matt black casing, because it absorbs infrared radiation before the radiation reaches the cable.
The glossy white casing, because it emits infrared radiation at a lower rate than the matt black casing.
Either casing, because objects at the same temperature emit infrared radiation at the same rate.
106 exam-style questions on AQA GCSE Physics 6.3 Black body radiation, covering 6.3.1 Emission and absorption of infrared radiation and 6.3.2 Perfect black bodies and radiation. Each one has a worked solution and a mark scheme showing where the marks go.