There are all sorts of electromagnetic waves. The shorter the wavelength the higher the energy of the waves. The energy from the sun is mostly visible but much of it is also ultraviolet and infrared.

Sometimes the particle nature of radiation is important and in those cases we refer to the photon energy. Looking at light as a bundle of particles (photons) each with a characteristic wavelength is useful when investigating cell mutations of photochemical effects. AN X-ray photon is much more damaging than a microwave photon.

• Micro meter = millionth of a meter

Micro meter = m

Visible light 0.4 m to 0.7 m comes from the sun.

Earth radiates invisible infrared radiation centered about the 10 m region of the electromagnetic spectrum.

The energy from the sun is mostly visible but much of it is also ultraviolet and infrared.

Wein’s Radiation Law. As temperature increases wavelength of maximum radiant intensity, max, increases.

max 3000(m K)

TK

Sun

Earth

T=6000 K

T=300 K

Earth has an average temperature of about 300 K.What is the wavelength of maximum energy emission from Earth? (Wien's Law)

Our Sun has an average temperature 6000 K.What is the wavelength of maximum energy emission from the sun? (Wien's Law) 

Radiation Laws

As temperature increases wavelength of maximum radiant intensity, max, increases.Wein’s Displacemnet Law.

max 3000(m K)

TK

max 3000(m K)

6000K0.5mSun

Earth max 3000(m K)

300K10.0m

If the temperature of Earth doubled to 600 KWhat is its new wavelength of maximum energy emissionafter its temperature doubles?

If the temperature of Earth doubled to 600 KWhat is its new wavelength of maximum energy emissionafter its temperature doubles?

Ans: 5.0 m

Stefan_Boltzman Radiation Law.

As temperature increases total radiation output increases.

Brightness = Intensity Energy leaving an object each sec per square meter

Intensity T4

As T double Brightness increases by ___??____

As T triples Brightness increases by _______

Radiation Laws

As temperature increases total radiation output increases. Stefan_Boltzman Radiation Law.

Brightness = Intensity Energy leaving an object each sec per square meter

Intensity T4

As T double Brightness increases by 16

As T triples Brightness increases by _81 times = 3x3x3x3__

Intensity T4

Black Body =1.0

The hole acts like a blackbody. All radiant energy is absorbed none is reflected. If the inside of the cavity were to become hot then the hole would glow.

Hotter object give off more radiation and radiation with shorter wavelengths.

The energy from the sun is mostly visible but much of it is also ultraviolet and infrared.

The atmosphere absorbes very little solar radiation but much of the outgoing long wave radiation radiating from earth’s surface.

Image modified from:http://www.usatoday.com/weather/tg/wghwrmng/wghwrmng.htm

Surface gets energy only from the sun when there is no atmosphere. Earth’s radiative equilibrium temperature would be about 255 K or 0.0 F

No Atmosphere

Solar In IR out

Surface gets solar energy from the sun and infrared energy from the atmosphere when there is an atmosphere. In this case earth’s global mean surface temperature is much warmer than without an atmosphere (288 K or 60 F)Image modified from:

http://www.usatoday.com/weather/tg/wghwrmng/wghwrmng.htm

With an Atmosphere

Radiative Equilibrium (When an object is in equilibrium, the rate of energy loss equals the rate of energy gain)

An objects absorbs energy at an average rate of 100 W/m2 and emitts energy at a rate of 120 W/m2. Will the temperature of this object increase, decrease, or stay the same?

An objects absorbs energy at an average rate of 120 W/m2 and emitts energy at a rate of 120 W/m2. Will the temperature of this object increase, decrease, or stay the same?

An objects absorbs energy at an average rate of 140 W/m2 and emitts energy at a rate of 120 W/m2. Will the temperature of this object increase, decrease, or stay the same?

Radiative Equilibrium (When an object is in equilibrium, the rate of energy loss equals the rate of energy gain)

An objects absorbs energy at an average rate of 100 W/m2 and emitts energy at a rate of 120 W/m2. Will the temperature of this object increase, decrease, or stay the same?

An objects absorbs energy at an average rate of 120 W/m2 and emitts energy at a rate of 120 W/m2. Will the temperature of this object increase, decrease, or stay the same?

An objects absorbs energy at an average rate of 140 W/m2 and emitts energy at a rate of 120 W/m2. Will the temperature of this object increase, decrease, or stay the same?

Kirchoff's radiation law

Good absorbers of radiation are also good emitters of radiation.

The idea her is that the molecular structure of a material that makes it a good receiver of radiation also make it a good transmitter.

Black absorbs energy vary well but black also cools off fast. 

Two identical pots of coffee are heated and then allowed to cool. Which cools faster a black pot of coffee or a shiny silver pot of coffee? 

Two identical pots of coffee are heated and then allowed to cool. Which cools faster a black pot of coffee or a shiny silver pot of coffee?