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Black Body Radiation Practice Questions

Question 1

4 marks

All objects emit and absorb infrared radiation.

(a)

Which statement describes a perfect black body?

Tick (✔) one box.

  • An object that reflects all of the radiation incident on it
  • An object that transmits all of the radiation incident on it
  • An object that absorbs all of the radiation incident on it
  • An object that emits no radiation at any temperature
(b)

State what happens to the amount of infrared radiation emitted each second by an object when the temperature of the object increases.

(c)

A student takes an ice cube at −8 °C-8\ \degree\text{C} out of a freezer.

The student says:

'The ice cube is too cold to emit any infrared radiation.'

The student is wrong.

Explain why.

Question 2

5 marks

A café owner tested four identical metal teapots. Each teapot had a different outer surface.

Each teapot was filled with 800 cm3800\ \text{cm}^3 of water at 90 °C90\ \degree\text{C} and left on the same bench.

The temperature of the water in each teapot after 20 minutes is shown in Table 1.

Table 1

Outer surface of teapot Temperature of water after 20 minutes in °C
Dull black 58
Shiny black 64
Dull white 68
Shiny white 74
(a)

Calculate the decrease in temperature of the water in the dull white teapot during the 20 minutes.

(b)

Give two conclusions about the emission of infrared radiation that can be made from the results in Table 1.

(c)

The café owner wants the tea to stay hot for as long as possible.

Which teapot should the owner use?

Give a reason for your answer.