Intensity

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

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

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

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

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 next