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Black body radiation: GCSE Combined Science Physics practice questions

Foundation and Higher · Grade 6

A second set of questions on black body radiation. They are different from the ones on the topic page. Try each, then open the answer and compare your working.

More questions

Question 1 Hard

Explain why the temperature of the Earth stays roughly steady.

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Answer: It is steady when the rate the Earth absorbs radiation equals the rate it emits radiation.

  1. The Earth absorbs radiation from the Sun.
  2. It also emits infrared, and the temperature is steady when the two rates are equal.

Question 2 Hard

Explain how adding greenhouse gases to the atmosphere affects the Earth’s temperature.

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Answer: They absorb outgoing infrared, so less escapes and the Earth warms until the rates match again.

  1. They absorb some outgoing infrared.
  2. Less escapes, so the Earth warms until absorbed and emitted radiation match again.

Question 3 Hard

Explain why a shiny silver flask keeps a hot drink hot.

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Answer: The shiny surface is a poor emitter of infrared, so less energy is radiated away.

  1. Shiny surfaces are poor emitters of infrared.
  2. Less radiation escapes, so the drink loses energy more slowly.

Question 4 Hard

Explain why the Sun emits visible light but a cold room emits only infrared.

Show answer

Answer: The Sun is much hotter, so it emits at shorter wavelengths, including visible light.

  1. Hotter objects emit at shorter wavelengths.
  2. The Sun is far hotter, so its peak is at visible wavelengths.

Quick checks

Short questions with options. Choose one before you open the answer.

Check 1

What type of radiation do all objects emit because of their temperature?

  1. Infrared radiation.
  2. Ultraviolet radiation.
  3. Gamma radiation.
Show answer

Infrared radiation. Every object emits infrared, even a cold one.

Check 2

What happens to the infrared an object emits each second when it gets hotter?

  1. It decreases.
  2. It stays the same.
  3. It increases.
Show answer

It increases. Hotter objects emit more infrared each second.

Check 3

Which type of surface is the best absorber of infrared radiation?

  1. A dull black surface.
  2. A shiny silver surface.
  3. A white surface.
Show answer

A dull black surface. Dull black surfaces take in the most radiation.

Check 4

Which type of surface is the best emitter of infrared radiation?

  1. A shiny silver surface.
  2. A dull black surface.
  3. A white surface.
Show answer

A dull black surface. A good absorber is also a good emitter.

Check 5

Which type of surface is the worst emitter of infrared radiation?

  1. A dull black surface.
  2. A matt grey surface.
  3. A shiny silver surface.
Show answer

A shiny silver surface. Shiny surfaces reflect most of the radiation and emit little.

Check 6

Why are shiny surfaces poor absorbers of infrared?

  1. They reflect most of the radiation that hits them.
  2. They give out all the radiation they take in.
  3. They are always too cold.
Show answer

They reflect most of the radiation that hits them. Reflected radiation is not absorbed.

Check 7

Why are solar heating panels painted dull black?

  1. To reflect the Sun’s radiation away.
  2. To absorb as much radiation as possible.
  3. To emit as little as possible.
Show answer

To absorb as much radiation as possible. More radiation absorbed means more energy to heat the water.

Check 8

Why does a shiny flask keep a drink hot?

  1. The shiny surface is a poor emitter, so little infrared escapes.
  2. The shiny surface absorbs all the heat.
  3. The shiny surface makes the drink hotter.
Show answer

The shiny surface is a poor emitter, so little infrared escapes. A flask loses energy slowly because shiny surfaces emit little.

Check 9

What is a perfect black body?

  1. An object that reflects all radiation.
  2. An object that emits no radiation.
  3. An object that absorbs all of the radiation that hits it.
Show answer

An object that absorbs all of the radiation that hits it. It does not reflect or transmit any radiation.

Check 10

What else is true of a perfect black body, as well as absorbing everything?

  1. It is the best possible emitter at its temperature.
  2. It emits no radiation at all.
  3. It always stays cold.
Show answer

It is the best possible emitter at its temperature. A perfect absorber is a perfect emitter.

Check 11

What does the radiation emitted by a black body depend on?

  1. What it is made from.
  2. Only its temperature.
  3. How big its surface colour is.
Show answer

Only its temperature. Temperature alone sets the pattern of radiation.

Check 12

What happens to the peak wavelength of a black body as it gets hotter?

  1. It gets longer.
  2. It does not change.
  3. It gets shorter.
Show answer

It gets shorter. Hotter bodies peak at shorter wavelengths, so they look yellow or white.

Check 13

What happens to the radiation emitted at each wavelength when a black body gets hotter?

  1. It increases at every wavelength.
  2. It decreases at long wavelengths.
  3. It stays the same.
Show answer

It increases at every wavelength. The whole curve gets taller as well as shifting left.

Check 14

When is the temperature of an object steady?

  1. When it stops absorbing radiation.
  2. When it absorbs and emits radiation at the same rate.
  3. When it stops emitting radiation.
Show answer

When it absorbs and emits radiation at the same rate. Equal rates mean no net change in energy.

Check 15

What happens to the temperature of an object that absorbs more than it emits?

  1. It rises.
  2. It falls.
  3. It stays the same.
Show answer

It rises. The object gains energy, so it warms.

Check 16

What happens to the temperature of an object that emits more than it absorbs?

  1. It rises.
  2. It stays the same.
  3. It falls.
Show answer

It falls. A net loss of energy means cooling.

Check 17

How do extra greenhouse gases change the temperature of the Earth?

  1. They absorb outgoing infrared, so the Earth warms.
  2. They reflect the Sun’s radiation, so the Earth cools.
  3. They make no difference.
Show answer

They absorb outgoing infrared, so the Earth warms. Less infrared escapes, so the Earth warms until the rates match.

Check 18

Name two greenhouse gases.

  1. Oxygen and nitrogen.
  2. Carbon dioxide and methane.
  3. Argon and helium.
Show answer

Carbon dioxide and methane. Water vapour is another greenhouse gas.

Check 19

Why can the Sun emit visible light when a cool room cannot?

  1. The Sun is much closer.
  2. A room cannot absorb light.
  3. The Sun is much hotter.
Show answer

The Sun is much hotter. Hotter objects emit shorter wavelengths such as visible light.

Check 20

Why are houses in hot countries often painted white?

  1. White surfaces reflect radiation, so the houses absorb less.
  2. White paint absorbs the most radiation.
  3. White paint makes the houses emit more.
Show answer

White surfaces reflect radiation, so the houses absorb less. Less absorbed radiation keeps the house cooler.

Check 21

In a Leslie cube test, what must you keep the same for a fair test?

  1. The colour of every face.
  2. The water temperature and the distance from the detector.
  3. Nothing. Only the detector matters.
Show answer

The water temperature and the distance from the detector. You change only the surface, and control everything else.

Check 22

What does an infrared camera detect?

  1. The infrared radiation that objects emit.
  2. The light that objects reflect.
  3. The sound that objects make.
Show answer

The infrared radiation that objects emit. Hotter objects look brighter in the picture.

Check 23

A student says only hot objects emit radiation. What is wrong with that?

  1. Nothing. Cold objects emit no radiation.
  2. Only dull black objects emit radiation.
  3. All objects emit infrared. Hotter objects emit more.
Show answer

All objects emit infrared. Hotter objects emit more. Every object emits infrared at any temperature above absolute zero.

Check 24

A student says a black body emits nothing because it looks black. What is wrong?

  1. A perfect black body is the best emitter.
  2. Nothing. Black bodies give out no radiation.
  3. A black body gives out only visible light.
Show answer

A perfect black body is the best emitter. Absorbing everything and emitting the most go together.

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