4.6.3.2 Perfect Black Bodies and Radiation

Question 1

What do all bodies (objects) do?

Answer 1

all bodies absorb and emit radiation

Question 2

What does the emission of radiation from an object depend on?

Answer 2

the intensity and wavelength of any emission depends on the temperature of the body

Question 3

What is a body at a constant temperature doing?

Answer 3

a body at a constant temperature is absorbing radiation at the same rate as it is emitting radiation

Question 4

What is happening when the temperature of a body is increasing?

Answer 4

• the temperature of a body increases when the body absorbs radiation faster than it emits radiation
• the intensity of every wavelength increases
• the shorter the wavelength, the more rapid the rise in intensity
• the peak intensity occurs at smaller wavelength

Question 5

What does the temperature of the Earth depend on?

Answer 5

• rates of absorption and emission of radiation
• reflection of radiation into space

Question 6

The Greenhouse Effect

Answer 6

• Earth absorbs IR radiation and re-emit at a longer wavelength (IR radiation)
• GHG’s absorb IR radiation and e-emit in all directions (Earth’s atmosphere warms)
• some IR radiation re-emitted by the Earth transmits through the atmosphere out to space

Question 7

What does the intensity and wavelength distribution of any emission depend on?

Answer 7

• the temperature of the body
• very hot objects emit shorter wavelength radiation than cooler objects → explain why very hot objects produce visible light e.g. a piece of very hot metal
• the intensity fo radiation also increases at high temperatures

Question 8

What happens if an object is warmer than its surroundings?

Answer 8

• emits more radiation than it absorbs
• so its temperature will decrease

Question 9

What happens if an object is cooler than its surroundings?

Answer 9

• object will absorb more radiation than it emits
• temperature will increase

Question 10

What are the only ways that the Earth can gain/lose energy?

Answer 10

absorbing or emitting radiation

Question 11

What does the Sun emit?

Answer 11

• the Sun emits short wavelength radiation such as visible light and UV
• this radiation travels to the Earth

Question 12

What does the Earth do with the radiation it receives from the Sun?

Answer 12

• some of the radiation is reflected by the clouds
• the remaining radiation can then be absorbed by the surface of the Earth
• causes temp of Earth to increase
• Earth than emits IR back to space
• however, some of E of IR is trapped by GHGs in the atmosphere e.g. CO2
• human activity is increasing levels of GHGs
• means more heat energy trapped in atmosphere and less is radiated into space

Question 13

What can affect how much energy is radiated from the Earth?

Answer 13

• many factors
• e.g. cloud cover - cloudy nights tend to be warmer than clear nights as clouds can reflect IR back to Earth and prevent it from being radiated into space