Environmental Geology – Notes Lecture Energy, EM Spectrum

Energy, Electromagnetic Spectrum, Heat Transfer and Energy Balance

Temperature: measure of the average molecular motion in a substance

• It is a measure of the kinetic energy (energy of motion)
• Greater motion = greater temperature

Measurement Scales:

1. Kelvin (K) 0 degrees K = absolute zero = no motion
2. Fahrenheit (degrees F): developed in 1700’s; 180 degrees between freezing (32 degrees) and boiling (212 degrees)
3. Celsius (degrees C): 0 freezing – 100 boiling

Conversions:

F = 1.8 C +32

F = 9/5 C = 32

C = (F-32)/1.8

C = 5/9 (F-32)

K = C + 273.15

Energy

• Light (radiant energy)
• Motion (kinetic energy)
• Energy of place (potential energy – example: gravity)
• Chemical energy

Radiant energy from the sun powers Earth’s climate system and powers our ecosystems

Sun fuses hydrogen to helium releasing energy in the process

Energy transfers through space as radiant energy in the form of Electromagnetic radiation (Electromagnetic Waves)

Waves move energy.

All things above absolute zero emit radiation

Wavelength of radiation emitted is a function of the objects temperature: higher temperature = shorter wavelengths. This relationship is described by Wein’s Law; wavelength = 2,897 (a constant) micrometers K/temperature (in degrees K)

Wavelength – designated by Greek letter lambda = distance between adjacent peaks or troughs

Radiant solar energy reaches the earth and is converted by photosynthesis and stored (chemical energy)

Different types of electromagnetic (EM) radiation are described by the EM spectrum

• Radio Waves (long waves, low frequency) 1 m to 1,000’s of meters

• Microwaves ( long waves) 1,000 micrometers to about 1 m

• Infrared (long waves) 0.7 micrometers to several hundred meters

• Visible light (the colors of the rainbow; short waves) 0.4 to 0.7 micrometers

• Ultraviolet (short waves)

• x-rays (short waves)

• Gamma rays (short waves)

On micrometer = one millionth of a meter = 10^-6 meters = 0.000001 m

Average visible light is about 0.0000005 m or 0.5 micrometers

Short wave EM radiation is dangerous: gamma rays kill, UV causes sun burns and skin cancer

About 90% of the suns energy is emitted in the visible light portion of the EM Spectrum

Less than 10% is in the shorter wave lengths (UV) 0.01 to 0.4 micrometers

Most solar radiation reaching the Earth is in the visible range (short wave – averaging 0.5 micrometers)

Most radiation from the Earth is in the infrared range (long wave – averaging about 10 micrometers).

Objects that have greater temperatures emit radiation at a greater rate

This relationship is defined by Stefan- Boltzman Law: E = sigma x Temperature (in degrees K)

E = amount of emitted radiation

Sigma is a constant = 5.735 x 10^-5 langleys/minute/degree

Using the relationship between Wein’s Law and the Stefan-Boltzman Law it can be shown that the sun emits about 200,000 times more.

The Earth’s atmosphere is relatively transparent to incoming short wave radiation (allows this to pass easily) but is relatively translucent to outgoing longwave radiation (captures much of the energy within the atmosphere).

Without the atmosphere the Earth would have much warmer days and cooler nights as a result of this phenomenon.

In addition, the upper portions of the atmosphere where the Ozone occurs (stratosphere) absorbs UV thus protecting us from even more burns and cancers.

Heat Transfer and Energy Balance

Heat is transferred to the Earth’s atmosphere by four primary mechanisms

1. radiation
2. conduction
3. convection
4. latent heat