1. Intensity

2. Energy Density Wave energy is proportional to amplitude squared.
Use the energy density u
u = ½ e0E2 = ½ B2/m0
Power is the time rate of change of energy.
Proportional to the speed
Proportional to amplitude squared

3. Power Volume
The power of a wave in a volume is related to the area and speed.

4. Intensity
Intensity of a wave is the rate energy is carried across a surface area.
Also called irradiance
This is true for linear and other waves.
For a spherical wave, the intensity I = P/A = P/4pr2

5. Plane Profile EM waves that intersect at an angle deliver less power.
The tilt of the earth changes the power received from the sun.

6. Laser
A 1.0 mW laser has a frequency of 4.74 x 1014 Hz. The cross sectional area is 3.14 x 10-6 m2.
Find the irradiance and the amplitude of the electric field.
The irradiance comes directly from the power and area.
I = P/A = 3.2 x 102 W/m2
The amplitude comes from the irradiance.
E = 0.49 kV/m
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