AQA GCSE Physics (8463), Higher tier · Waves › Black body radiation
Practise Perfect black bodies and radiation. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Scientists use the idea of a perfect black body to describe how objects absorb and emit radiation. What is a perfect black body?
An object that absorbs all the radiation that falls on it.
State whether a perfect black body is a good or a poor emitter of radiation, for its temperature.
A good emitter (the best possible emitter for its temperature).
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Scientists use the idea of a perfect black body to describe how objects absorb and emit radiation.
(a) What is a perfect black body?[1]
(b) A perfect black body does not reflect any of the radiation that falls on it. Name one other thing that a perfect black body does not do to incident radiation.[1]
(c) Explain why a perfect black body would be the best possible emitter of radiation.[1]
(d) The intensity and the wavelength distribution of the radiation emitted by a body depend on one property of the body. Which property? Tick (✓) one box.[1]
Its mass
Its temperature
Its volume
Its weight
Show the answer and mark scheme
(a)Answer: An object that absorbs all the radiation that falls on it.
an object that absorbs all of the radiation incident on it
(b)Answer: Transmit it
transmit (it)
(c)Answer: Good absorbers are good emitters, and it is the best possible absorber.
a good absorber is also a good emitter, and a perfect black body is the best possible absorber
(d)Answer: Its temperature
Question 2Medium6 marks
A car is parked in bright sunshine. The temperature inside the car increases for a while and then stays constant.
(a) Explain why the temperature of the car increases at first.[2]
(b) Explain why the temperature of the car eventually stays constant.[2]
(c) A cloud covers the Sun. Describe and explain what happens to the temperature of the car.[2]
Show the answer and mark scheme
(a)Answer: It absorbs radiation faster than it emits it, so its temperature rises.
the car absorbs radiation faster than it emits radiation
so its internal energy / temperature increases
(b)Answer: As it gets hotter it emits radiation faster, until emission equals absorption.
as its temperature increases, the car emits radiation at a greater rate
until it emits radiation at the same rate as it absorbs radiation
(c)Answer: It falls, because the car now emits radiation faster than it absorbs it.
the temperature decreases
the car now absorbs radiation more slowly than it emits radiation
Question 3Hard6 marks
The temperature of the Earth depends on the balance between the radiation it absorbs and the radiation it emits.
Explain how the temperature of the Earth's surface and atmosphere depends on the absorption, emission and reflection of radiation. Include in your answer what would happen to the Earth's temperature if the amount of ice at the poles decreased.[6]
Show the answer and mark scheme
Answer: Level-of-response answer: absorbed − emitted radiation determines temperature change; reflection by ice and clouds and absorption of infrared by atmospheric gases affect the balance; less ice means more absorption and a higher equilibrium temperature.
radiation from the Sun (mainly visible light and infrared) reaches the Earth
some of this radiation is reflected back into space by clouds, ice and snow
the rest is absorbed by the Earth's surface and atmosphere, which increases their temperature
the Earth's surface emits infrared radiation
some of this infrared is absorbed by gases in the atmosphere (e.g. carbon dioxide, water vapour, methane) and re-emitted, some back towards the surface
the temperature is constant when radiation is absorbed at the same rate as it is emitted (into space)
if radiation is absorbed faster than it is emitted, the temperature rises
less ice means less radiation is reflected, so more is absorbed
so the temperature rises until the rate of emission increases to match the new rate of absorption
Marked with levels of response: the full level descriptors are in the app.