Energy and Radiation Laws

Question 1

Energy

Answer 1

the ability to do work, and work is done when a unit force acts over unit distance.

Question 2

Forms on energy in atmosphere

Answer 2

Radiant energy - electromagnetic waves (Sun, hot fire, clouds, any
object)
- Sensible heat – thermal energy we can feel (warm air)
- Latent heat – due to phase changes of a substance, especially water
(cooling we feel after getting out of the swimming pool)

Question 3

Thermodynamics:

Answer 3

Physics that deals with the relationships and conversions

between heat and other forms of energy.

Question 4

Conservation of energy:

Answer 4

Energy can be neither created nor

destroyed, but can be converted from one form to another.

Question 5

Energy balance:

Answer 5

Within a system all inflows and outflows of

energy and mass have to balance.

Question 6

Radiant energy, in the form of electromagnetic

waves…

Answer 6

is emitted at the speed of light by all objects with a

temperature above absolute zero (-273° C)

Question 7

Electromagnetic radiation

Answer 7

• Emitted from all matter
• has a wide spectrum of wavelengths
• Can travel in a vacuum (space)
• Travels in straight lines
• Travels at C=3 x 108 m s-1
  (speed of light). e.g. it takes 8
  min 20 s for radiation to travel from the Sun to the Earth

Question 8

Wavelength

Answer 8

distance between crests in mm

Question 9

Planck’s Law

Every:

Answer 9

object emits radiation at all times and at all
wavelengths.
- gives the amount of blackbody monochromatic (single wavelength) radiative flux, called
irradiance,

Question 10

Wien’s Law

States:

Answer 10

the wavelength of maximum emission

from a blackbody is inversely proportional to its absolute T of its surface

Question 11

Kirchhoff’s Law

Answer 11

assuming no transmission the absorptivity of a body equals its emissivity

Question 12

Stefan-Boltzmann Law

Answer 12

• The total energy emitted by a blackbody is proportional to
  the fourth power of its absolute T:
• Natural objects are not full radiators. The emittance from
  these objects (called grey bodies)

Question 13

What does an infrared thermometer do?

Answer 13

It uses the uses the Stefan-Boltzmann
law and can be used to
measure the surface
temperature of objects

Question 14

Thick clouds on a satellite image look:

Answer 14

bright white

Question 15

thin clouds on a satellite image look:

Answer 15

greyish

Question 16

Bright clouds mean:

Answer 16

cold and a higher top

Question 17

Feathery, not too bright and relatively thin clouds that appear white mean…

Answer 17

They have cold tops and are categorized as cirrus

Question 18

Fairly bright, modestly thick clouds with a greyish appearance means…

Answer 18

They are low clouds and can be classified as stratocumulus

Question 19

Solar constant:

Answer 19

the solar radiant flux density (irradiance) at top of Atmosphere, normal to solar beam, at Earth’s mean distance from
Sun

Question 20

Cosine law of radiation

Answer 20

Describes how the incident radiant flux density of a
beam decreases as the beam’s angle varies from overhead
(normal) to a more slanted path relative to the surface

Question 21

What surface properties control incident

radiation?

Answer 21

• absorptivity: fraction of incident radiation
  absorbed
• reflectivity: fraction reflected from the surface
• transmissivity: fraction transmitted through the
  surface

Question 22

Absorption:

Answer 22

the full energy transfer from

radiation to a substance

Question 23

Atmospheric absorption varies by

substance:

Answer 23

UV – absorbed by O3
(stratosphere)
Visible – hardly absorbed
Infrared – partially absorbed by water
vapour, CO2

Question 24

Scattering

Answer 24

– the deflection of radiation

by a substance

Question 25

Diffuse scattering

Answer 25

– radiation deflected
in many directions, becomes diffuse
radiation

Question 26

Reflection

Answer 26

– a type of scattering,
radiation is deflected back with equal
intensity (mirror)

Question 27

Albedo

Answer 27

– the fraction of light reflected

earth’s albedo is ~0.3

Question 28

Lowest albedos

Answer 28

(best absorbers) are open water, organic soils,
coniferous forest (0.03-0.15)

Question 29

Highest albedos

Answer 29

(poor absorption) are snow, ice, dry light soils,
desert sand (0.35-0.95)

Question 30

Intermediate albedos

Answer 30

deciduous forest (0.15-0.2), agricultural
crops (0.2-0.25)

Question 31

Scattering affects:

Answer 31

• The blue sky and red sunsets 
(Rayleigh scattering)
• Hazy or polluted days making the sky white
or gray (Mie scattering)
- White clouds (nonselective scatterin

Question 32

Rayleigh

scattering

Answer 32

the smallest
gaseous
molecules and
aerosols responsible for
blue sky and red
sunsets

Question 33

Mie

scattering

Answer 33

by
larger particles
(e.g. water
droplets).
Produces hazy
and whiter
skies. Heavy
aerosol
pollution
causes even
redder sunset

Question 34

non-selective scattering

Answer 34

• bigger particles
• individual droplets:
  refraction ➔ rainbow