The average surface temperature of a planet has been constant for many years. Which statement about the planet must be true over that time?
It absorbs radiation at the same rate as it emits radiation.
It absorbs no radiation, because all of the radiation is reflected.
It emits radiation at a greater rate than it absorbs radiation.
It emits radiation of exactly the same wavelength as it absorbs.
40 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.