Explain that all objects emit and absorb infrared radiation, hotter objects emit more, and a perfect black body is the best absorber and emitter, reflecting or transmitting none.
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GCSE Physics Revision
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GCSE Physics revision
Emission and absorption of infrared radiation
Black body radiation (physics only)
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AQA student objectives
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Apply the specified scientific knowledge of emission and absorption of infrared radiation to a relevant example.
Analyse an unfamiliar example of emission and absorption of infrared radiation using the specified scientific ideas.
Revision summary
Key knowledge
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All Objects Emit and Absorb Infrared Radiation
- Every object — living or non-living, metal or non-metal, big or small — constantly emits and absorbs infrared waves.
- Because infrared waves are emitted in all directions, nearby objects can exchange infrared radiation with each other simultaneously.
- An object both absorbs infrared waves from its surroundings and emits its own infrared waves at the same time.
Emitting Infrared Radiation
- When an object emits infrared radiation, it loses internal energy, causing its temperature to decrease.
- This cooling effect is easy to observe in everyday situations, such as a hot meal cooling down or a warm person standing in a cold room.
- An electric heater is a deliberate use of infrared emission — electric current raises the heater's temperature, and it releases this energy by emitting infrared waves.
Absorbing Infrared Radiation
- When an object absorbs infrared radiation, it gains internal energy, causing its temperature to increase.
- A practical example is warming yourself near an electric heater, as your body absorbs the infrared waves it emits.
- Ice melting in a warm room is another example of an object absorbing infrared radiation and gaining internal energy.
Infrared Radiation in Cooking
- An oven produces a high intensity of infrared waves, which are absorbed by food such as a potato, increasing its internal energy.
- The absorbed infrared radiation raises the food's temperature to the point where it cooks, demonstrating a practical application of infrared absorption.
- Even while absorbing infrared waves inside the oven, the potato continues to emit its own infrared radiation simultaneously.
Key Relationships: Temperature and Internal Energy
- Objects with higher temperatures possess greater internal energy, which is why hotter objects emit infrared radiation at a greater rate.
- Emitting infrared radiation decreases an object's internal energy and temperature, whilst absorbing it increases both.
GCSE Exam Focus: What You Need to Know
- For your GCSE exam, you must understand that all objects both absorb and emit infrared radiation continuously.
- You do not need to explain why infrared waves specifically are emitted and absorbed, only that this process occurs for all objects.
- Key vocabulary to remember includes: infrared radiation, electromagnetic wave, internal energy, emit, and absorb.