6.3.1Emission and absorption of infrared radiation
AQA GCSE Physics (8463), Higher tier · Waves › Black body radiation
Practise Emission and absorption of infrared radiation. 19 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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Two identical metal blocks are at temperatures of 20 °C and 80 °C. Which block emits more infrared radiation each second?
The block at 80 °C
Give two factors that affect how much infrared radiation a surface emits each second.
Temperature and the type of surface (colour/texture).
State whether a matt black surface is a good or a poor emitter of infrared radiation.
A good emitter.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
All objects emit and absorb infrared radiation.
(a) Which statement is correct? Tick (✓) one box.[1]
Only hot objects emit infrared radiation.
All objects emit infrared radiation, whatever their temperature.
Cold objects absorb infrared radiation but never emit it.
Objects only emit infrared radiation when they glow.
(b) Two identical metal blocks are at temperatures of 20 °C and 80 °C. Which block emits more infrared radiation each second?[1]
(c) Give one example of an object that emits infrared radiation but does not glow.[1]
(d) Name one device that detects infrared radiation.[1]
Show the answer and mark scheme
(a)Answer: All objects emit infrared radiation, whatever their temperature.
(b)Answer: The block at 80 °C
the block at 80 °C / the hotter block
(c)Answer: A person (or a hot drink, or a radiator).
a person / a hot drink / a warm radiator / an animal / an iron
(d)Answer: An infrared (thermal imaging) camera.
infrared camera / infrared thermometer / infrared detector / thermal imaging camera
Question 2Medium5 marks
A student is investigating how the type of surface affects the rate of emission of infrared radiation, using a Leslie cube and a detector.
(a) Give two variables the student should keep the same for each surface, to make this a fair test.[2]
(b) The student fills the cube with hot water once, and then tests the four surfaces at 5-minute intervals. Explain why this could give unfair results, and suggest how the student could avoid the problem.[3]
Show the answer and mark scheme
(a)Answer: Any two: the water temperature when reading, the detector's distance from the surface, and the timing.
the temperature of the water in the cube each time a reading is taken
the distance between the detector and the surface
the length of time the reading is taken over
the volume of water in the cube
(b)Answer: The cube cools between tests, so later surfaces give unfairly low readings; take all four readings quickly one after another (or refill with water at the same temperature before each test).
the water (and the cube) cools down during the investigation, so later surfaces are tested at a lower temperature
a surface tested later would give a lower reading, not because it is a poorer emitter but because the cube is cooler by then
take the readings for all four surfaces quickly, one straight after another (while the temperature is the same) / refill with hot water at the same starting temperature before testing each surface
Question 3Hard5 marks
A student uses a Leslie cube and a detector to compare the infrared emission of different surfaces. The detector is held by hand at approximately the same distance from each surface, judged by eye.
(a) Evaluate this method of positioning the detector, and suggest an improvement.[3]
(b) The detector also picks up infrared radiation from the student's own hand and body. Explain why this could affect the results, and suggest how to reduce the effect.[2]
Show the answer and mark scheme
(a)Answer: Holding it by hand risks small, uncontrolled differences in distance that would affect the readings; a clamped detector at a fixed, measured distance would be more reliable.
judging the distance by eye is likely to introduce random error, since the exact distance will vary slightly each time
because the detector reading depends strongly on distance, even a small difference in distance could change the reading enough to affect the comparison between surfaces
the student should fix the detector at a measured, marked distance (e.g. using a clamp and a ruler) for every surface, instead of holding it by hand
(b)Answer: The student's own body also emits infrared, which could add to the reading; mounting the detector on a stand away from the body reduces this.
the body emits infrared too, so some of the detector's reading may come from the student rather than from the cube's surface, making readings less accurate
keep the hand (and body) as far from the detector as practical, e.g. by mounting the detector on a stand instead of holding it