Summary
- Maxwell's equations
- Electromagnetic waves
- Doppler effect
- EM wave intensity
Today's joke
- Quiz Bonus Ch. 23
- Polarization of light
- Lecture learning outcomes
A student who masters the topics in this lecture will be able to:
- describe the polarization direction of a light wave in terms of the direction of the electric field
- describe how light can be polarized by reflection, scattering, or by polaroid material
- use algebra to find the transmitted intensity I, initial intensity I0, or angle θ between the polarization direction and the transmission axis of a polaroid filter when any two of these quantities are given
Practice:
Try these additional examples
Example #4
Example #5
Prepare:
Read textbook section 26-1 before the next lecture
gc6 tb 21.14
A bar magnet falls straight down through a loop of wire with the north pole entering first. As the north pole enters the loop, the induced
current will be (as viewed from above)
A. zero
B. clockwise
C. counterclockwise
Answer
POP5 24.qq.7
A polarizer for microwaves can be made as a grid of parallel metal wires about a centimeter apart. How is the
electric field vector oriented for microwaves transmitted through this polarizer?
A. parallel to the wires
B. perpendicular to the wires
C. 45° relative to the wires
D. circularly polarized
Answer
Walker5e 25.75
Unpolarized light is incident on a polarizer as indicated above. It then falls on an analyzer whose transmission
axis is at an angle θ to the vertical. Which graph depicts the transmitted intensity as θ
is changed from 0° to 360°?
Answer
POP5 24.45
A light beam of intensity I0 is polarized parallel to the transmission axis of a single
polarizing filter. Through what angle θ should the polarizer be rotated to reduce the
transmitted intensity I to I0/5?
A. 63.4°
B. 54.7°
C. 18.0°
D. 78.4°
Answer
Walker5e 25.EYU.5
In the system shown below a vertically polarized incident beam of light encounters two polarizers. If polarizer 1 is removed from the system, the intensity of the transmitted beam will ______.
A. increase
B. decrease
C. stay the same
Answer
Walker5e 25.73
Unpolarized light passes through two polarizers whose transmission axes are at an angle of 30.0° with respect to each other. What fraction of the incident intensity is transmitted through the polarizers?
A. 0.500
B. 0.707
C. 0.866
D. 0.375
Answer
C. counterclockwise
By Lenz's law the loop will attempt to produce a magnetic field pointing upward in order to oppose the downward pointing field of the falling magnet. Use the right hand rule to verify the current must flow counterclockwise in order to produce the opposing magnetic field.
B. perpendicular to the wires
The electric field parallel to the wires will drive current in the wire,
which will dissipate energy as heat due to Ohmic resistance. Therefore, the electric field component
parallel to the wires will be extinguished, but the perpendicular component will pass through the grid.
Graph B
The transmission axes will be aligned at 0°, 180°, and 360°
and permit the maximum transmitted intensity at those angles.
A. 63.4°
A. increase
With polarizer 1 in place the incident intensity is first cut in half (due to the 45° angle) and then reduced to zero (because the beam arrives at polarizer 2 with its plane of polarization rotated 90° with respect to the transmission axis). When polarizer 1 is removed the beam arrives at polarizer 2 with its plane of polarization rotated 45° with respect to the transmission axis, and the transmitted beam has half the incident intensity. Therefore, the effect of removing polarizer 1 is to increase the transmitted intensity from zero to 0.50I0.
D. 0.375
