Topic 5.15-5.19 — Radiation

Question 1

Describe the relationship between temperature and radiation

Answer 1

All bodies emit radiation. As temperature increases, the wavelength decreases and the intensity increases.

Question 2

How can a body retain a constant temperature?

Answer 2

For a body to be at a constant temperature it needs to radiate the same average power that it absorbs

Question 3

What happens to a body if the average power it radiates is less than the average power that it absorbs?

Answer 3

If it emits less power than it absorbs, the temperature will increase

Question 4

What happens to a body if the average power it radiates is more than the average power that it absorbs?

Answer 4

If it emits more power than it absorbs, the temperature will decrease

Question 5

Describe the relationship that explains how radiation affects the temperature of the Earth

Answer 5

The temperature of the earth is maintained by the amount of energy received and emitted from the sun.

Question 6

Explain how the temperature of the Earth is affected by factors controlling the balance between incoming radiation and radiation emitted

Answer 6

-Visible light and short wavelength, high frequency infra-red radiation from the sun is absorbed by the surface of the Earth (some is reflected by the atmosphere) and the planet’s internal energy increases and the surface gets hotter. Some of this energy is transferred to the atmosphere by conduction and convection.
The earth radiates lower frequency infra-red radiation, some of which is absorbed by greenhouse gases in the atmosphere which keeps the earth warm. The greenhouse gases emit infrared radiation, some towards Earth, which is then reabsorbed.

Question 7

Describe the core practical to investigate how the nature of a surface affects the amount of thermal energy radiated or absorbed

Answer 7

-Place a Leslie cube on a heat-resistant mat. Almost fill it with boiling water and replace the lid.

-Leave for one minute. This is to enable the surfaces to heat up to the temperature of the water.

-Use the infrared detector to measure the intensity of infrared radiation emitted from each surface, or the temperature of the surface. Make sure that the detector is the same distance from each surface for each reading.
(One surface is matt black, another matt white, another shiny black, another shiny silver)

-Plot a bar chart of Infrared radiation (W/m²) on the y-axis to Type of surface on the x-axis