Radiation

Question 1

How do you convert Kelvin to Celcius?

Answer 1

x°C = (273.15 + x) K

Question 2

What is a blackbody?

At what temperature does an object emit radiation?

Answer 2

A blackbody is an object that can absorb all the energy it receives, and it can also emit all the energy that it stores.

All objects emit radiation as long as they have a temperature greater than 0 K.

Question 3

What is the temperature of the sun, the Earth’s atmosphere, and the Earth’s surface?

Answer 3

Sun - 6000K
Surface of Earth’s atmosphere - 255K
Surface of Earth’s surface - 288K

Question 4

What is the formula for the Planck’s blackbody radiation curve?

Answer 4

I = σT^4

I - intensity of light / power
σ - Stefan Boltzmann constant (5.67 x 10^-8)
T - temperature in K

Question 5

As temperature increases, radiative power peaks at shower wavelengths. What is the equation for the wavelength?

Answer 5

λmax = b / T

b - Wein’s constant (3 x 10^-3)
T - temperature in K

Question 6

What is short-wave radiation?

What is long-wave radiation?

Answer 6

Solar radiation from the sun is called short-wave radiation. It peaks in the visible spectrum (390 - 700mm)

Terrestrial radiation from Earth is called long-wave radiation. It peaks in the infrared spectrum (10μm).

Both the sun and the Earth are almost blackbodies.

Question 7

How does the greenhouse gases in the atmosphere absorb radiation?

Answer 7

• trace gases with molecules comprising of 3 or more atoms resonate well with light waves and absorb them (e.g. H2O, CO2, CH4, O3)
• H2O also absorb waves that resonate with radiation waves (through rotation and vibration of the molecules)

Question 8

What are the known absorption bands of ozone, oxygen, water vapour and carbon dioxide?

Answer 8

ozone - visible, UV, and near infrared bands
oxygen - visible and near infrared bands
water vapour - near and far infrared bands
carbon dioxide - infrared bands at 14μm

atmospheric window (where radiation can escape from Earth) - 5 to 15μm

Question 9

What are the important greenhouses that affects radiation absorption and global warming?

Answer 9

Water vapour (1 - 4%) - absorbs most of the infrared radiation emitted by the Earth's surface and atmosphere
Carbon dioxide - absorbs within the narrow band of the atmospheric window that contributes to the few degrees of global warming
Ozone - abundant in the stratosphere and responsible for the temperature inversion there