Transcript Dispersion and Polarization (7/30)

Chapter 33
{
© 2012 Pearson Education, Inc.
The Nature and Propagation of Light (cont.)
Dispersion
•
•
Dispersion: The index of
refraction depends on the
wavelength of the light. See
Figure 33.18 (right).
Figure 33.19 (below) shows
dispersion by a prism.
© 2012 Pearson Education, Inc.
Rainbows—I
•
The formation of a rainbow is due to the combined effects
of dispersion, refraction, and reflection. (See Figure 33.20
below and on the next slide.)
© 2012 Pearson Education, Inc.
Rainbows—II
© 2012 Pearson Education, Inc.
Q33.4
Light passes from a medium of index of refraction na into a
second medium of index of refraction nb. The critical angle for
total internal reflection is qcrit.
In order for total internal reflection to occur, what must be true
about na, nb, and the incident angle qa?
A. na > nb and qa > qcrit
B. na > nb and qa < qcrit
C. na < nb and qa > qcrit
D. na < nb and qa < qcrit
© 2012 Pearson Education, Inc.
A33.4
Light passes from a medium of index of refraction na into a
second medium of index of refraction nb. The critical angle for
total internal reflection is qcrit.
In order for total internal reflection to occur, what must be true
about na, nb, and the incident angle qa?
A. na > nb and qa > qcrit
B. na > nb and qa < qcrit
C. na < nb and qa > qcrit
D. na < nb and qa < qcrit
© 2012 Pearson Education, Inc.
Polarization
•
•
An electromagnetic
wave is linearly polarized
if the electric field
always points along one
direction.
Figure 33.23 at the right
shows a Polaroid
polarizing filter.
© 2012 Pearson Education, Inc.
Malus’s law
•
•
•
•
Figure 33.25 below shows a polarizer and an analyzer.
Malus’s law: I = Imaxcos2.
Read Problem-Solving Strategy 33.2.
Follow Example 33.5.
© 2012 Pearson Education, Inc.
Q33.5
Three polarizing filters are stacked with the polarizing axes of
the second and third filters oriented at 45° and 90°, respectively,
relative to the polarizing axis of the first filter. Unpolarized
light of intensity I0 is incident on the first filter. The intensity of
light emerging from the third filter is
A. I 0 .
B. I 0 / 2.
C. I 0 / 2.
D. I 0 / 4.
E. I 0 / 8.
© 2012 Pearson Education, Inc.
A33.5
Three polarizing filters are stacked with the polarizing axes of
the second and third filters oriented at 45° and 90°, respectively,
relative to the polarizing axis of the first filter. Unpolarized
light of intensity I0 is incident on the first filter. The intensity of
light emerging from the third filter is
A. I 0 .
B. I 0 / 2.
C. I 0 / 2.
D. I 0 / 4.
E. I 0 / 8.
© 2012 Pearson Education, Inc.
Polarization by reflection
•
When light is reflected at the polarizing angle qp, the reflected
light is linearly polarized. See Figure 33.27 below.
© 2012 Pearson Education, Inc.
Brewster’s law
•
•
Brewster’s law:
tan qp = nb/na.
At the polarizing
angle, the reflected
and refracted rays are
perpendicular to each
other. See Figure
33.28 at the right.
© 2012 Pearson Education, Inc.
Q33.6
Natural light is incident on the surface of a liquid.
The reflected light will be completely polarized if
the incident angle qa is
A. greater than the polarizing angle.
B. greater than or equal to the polarizing angle.
C. equal to the polarizing angle.
D. less than or equal to the polarizing angle.
E. less than the polarizing angle.
© 2012 Pearson Education, Inc.
A33.6
Natural light is incident on the surface of a liquid.
The reflected light will be completely polarized if
the incident angle qa is
A. greater than the polarizing angle.
B. greater than or equal to the polarizing angle.
C. equal to the polarizing angle.
D. less than or equal to the polarizing angle.
E. less than the polarizing angle.
© 2012 Pearson Education, Inc.
Circular polarization
•
Circular polarization results from the superposition of two
perpendicularly polarized electromagnetic waves having equal
amplitude but a quarter-cycle phase difference. The result is
that the electric field vector has constant amplitude but rotates
about the direction of propagation. (Figure 33.30 below.)
© 2012 Pearson Education, Inc.
Scattering of light
•
•
Scattering occurs when light has been absorbed
by molecules and reradiated.
Figure 33.32 below shows the effect of scattering
for two observers.
© 2012 Pearson Education, Inc.
Why are clouds white?
•
Clouds are white because they scatter all wavelengths
efficiently. See Figure 33.33 below.
© 2012 Pearson Education, Inc.