Chapter 24 Electromagnetic Waves. Maxwell’s Equation (Two Versions)

Chapter 24Electromagnetic Waves

Maxwell’s Equation(Two Versions)

Electromagnetic Wave

EB

Light is represented by fluctuations in the magnetic and electric field called electromagnetic waves. EM wave is a consequence of the Maxwell’s Equation.

Basic Facts about EM waves in vacuum

• Always travels at exactly the speed of light c.• E and B are always perpendicular.• E×B gives the direction of the wave.• |E|=|cB|• Two independent direction of polarization (later)

The electromagnetic spectrum

Why do we see colors?

Question

This is precisely the speed of light! Conclusive proof that light is a kind of EM wave.

Bible?And God said, Let there be light,and there was light.- Genesis 1:3

Light as a wave

From this equation you can figure out the frequency from the wavelength or vice versa. You will do this many times in HW 24.

Polarization (no need to memorize)

Circular Polarization (Skip)Combination of vertical and horizontal polarization

Polarizing Filters

Electrons on long polymers (long molecules) that moves only in one direction, hence absorbing energy of the E field in that direction, but let the other direction through.

Two filters

Intensity Rules for Polarizer

Make sure you know whether the light is polarized or unpolarized!

Example with two filters

Polarization by Reflection

At the Brewster angle (or polarizing angle) θp, the reflected beam becomes polarized.

Brewster’s AngleComplete polarization by reflection occurs when the reflected beam is perpendicular to the refracted beam.

Brewster’s AnglePictures taken with polarizers at different angles. The picture on the right has the reflected light removed by the polarizer to minimize reflection.

Polarization by Scattering

Huygen’s PrincipleEvery point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of wave. The final wave is the sum of all these secondary wavelets.