Physlet Illustration: Polarization and Electromagnetic Waves
θ = °

In this simulation, an electromagnetic wave is propagating in the z direction and passing through a polarizer. The electric field is shown in blue. (The magnetic field is not shown.) The gray square represents the polarizer, and the black line shows its direction of polarization. You control the angle (0° < θ  < 90°)  between the initial wave's E field and the polarizer. You may also click-drag in the animation to change the viewing angle.  What fraction of the intensity passes through the polarizer? Why?

Hints:

  1. Rotate the animation, and verify the value of the angle θ  between the direction of the initial wave's E field and the direction of the polarizer axis.
  2. Find the cosine of that angle.
  3. Pause the animation and carefully rotate in order to measure the amplitude of the E field before the wave passes through the polarizer. (Be sure you have the field  lines oriented in the plane of the screen. You may need a ruler to measure the maximum amplitude.)
  4. Rotate again, in order to measure the amplitude of the E field after the wave passes through the polarizer.
  5. Find the ratio between these two amplitudes. How does it compare to cos(θ)?
  6. Remember that the intensity is proportional to the square of the electric field amplitude.

Reference

See The New Cosmic Universe, Section 33.6

Illustration written by Steve Mellema