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Flashcards in Energy and Radiation Laws Deck (34)
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1

Energy

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

2

Forms on energy in atmosphere

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)

3

Thermodynamics:

Physics that deals with the relationships and conversions
between heat and other forms of energy.

4

Conservation of energy:

Energy can be neither created nor
destroyed, but can be converted from one form to another.

5

Energy balance:

Within a system all inflows and outflows of
energy and mass have to balance.

6

Radiant energy, in the form of electromagnetic
waves...

is emitted at the speed of light by all objects with a
temperature above absolute zero (-273° C)

7

Electromagnetic radiation

- 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

8

Wavelength

distance between crests in mm

9

Planck’s Law
Every:

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

10

Wien’s Law
States:

the wavelength of maximum emission
from a blackbody is inversely proportional to its absolute T of its surface

11

Kirchhoff's Law

assuming no transmission the absorptivity of a body equals its emissivity

12

Stefan-Boltzmann Law

- 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)

13

What does an infrared thermometer do?

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

14

Thick clouds on a satellite image look:

bright white

15

thin clouds on a satellite image look:

greyish

16

Bright clouds mean:

cold and a higher top

17

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

They have cold tops and are categorized as cirrus

18

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

They are low clouds and can be classified as stratocumulus

19

Solar constant:

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

20

Cosine law of radiation

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

21

What surface properties control incident
radiation?

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

22

Absorption:

the full energy transfer from
radiation to a substance

23

Atmospheric absorption varies by
substance:

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

24

Scattering

– the deflection of radiation
by a substance

25

Diffuse scattering

– radiation deflected
in many directions, becomes diffuse
radiation

26

Reflection

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

27

Albedo

– the fraction of light reflected
(earth’s albedo is ~0.3)

28

Lowest albedos

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

29

Highest albedos

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

30

Intermediate albedos

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