1. Electromagnetic Waves-Ch 25 Wave Optics—Interference --Ch 17
Lecture 25
Electromagnetic Waves-Ch 25
Wave Optics—Interference --Ch 17

3. Problems for Wednesday
25: 19, 22, 28, 29, 31
WB 25: 13-18

4. Electromagnetic Waves
Slide 25-33

5. Sinusoidal Waves
Single frequency (single color) and single wavelength, λ.
TRANSVERSE with B and E perpendicular to the direction of motion.
In vacuum velocity = c = 3.00 x 108 m/s
Right hand rule relates E, B and direction of propagation
E = cB

6. Sinusoidal Waves Continued
Wave traveling in the +x direction with E polarized along the y-axis, and hence B along the z-axis.

7. Sinusoidal Waves continued
In vacuum,
wave speed is c = 3.00x108 m/s
λ= wavelength (spatial period)
T = (temporal) period
fλ = c

8. Intensity
Intensity—power incident on area A divided by A
Point Source

9. Polarization
Linear or plane polarization: The electric field oscillates along a straight line, the y-axis in our previous example.
A polarizer chooses a direction (called the polarizer axis) along which the transmitted E-field oscillates.
First polarizers reduces intensity by ½

10. Photons
Light particles: In some experiments, photo-electric effect for example, light acts like a particle.
Energy carried by each photon

11. Checking Understanding
A plane electromagnetic wave has electric and magnetic fields at all points in the plane as noted below. With the fields oriented as shown, the wave is moving
A. into the plane of the paper.
B. out of the plane of the paper.
C. to the left.
D. to the right.
E. toward the top of the paper.
F. toward the bottom of the paper.
Answer: A
Slide 25-34

12. Polarization
Slide 25-37

13. Light passed through a polarizing filter has an intensity of 2. 0 W/m2
Light passed through a polarizing filter has an intensity of 2.0 W/m2. How should a second polarizing filter be arranged to decrease the intensity to 1.0 W/m2?
Slide 25-38

14. The Electromagnetic Spectrum
Slide 25-39

15. Problems 25: 19 E = 10 V/m in an electromagnetic wave. What is B? 22:
What is λ, f, and electric field amplitude?
28: I = 10 W/m2 for a linearly polarized wave. Intensity through polarizer with b) θ = 300 ?

16. More Problems
29: 25% passes polarizer. Angle of polarizer with respect to electric field?
31: Unpolarized light with I = 350 W/m2
What is I after two polarizers with second axis 350 to axis of first?

17. Chapter 17 Wave Optics Topics: Sample question:
Double-slit interference
Diffraction gratings
Thin-film interference
Single-slit diffraction
Circular-aperture diffraction
Sample question:
The vivid colors of this hummingbird’s feathers have a sheen unlike that of ordinary pigments, and they change subtly depending on the angle at which they’re viewed. How does light interact with the feathers to produce this bright display?
Slide 17-1

18. Water Waves Spread Out behind a Small Opening
Slide 17-6

19. Light Waves Also Spread Out Behind a Very Narrow Slit
Slide 17-7

20. Young’s Double-Slit Interference Experiment
Slide 17-8

21. Analyzing the Double-Slit Experiment
Slide 17-9

22. Bright and Dark Fringes in the Double-Slit Experiment
Slide 17-10

23. Problems 17 CQ1: frequency in water, glass
CQ3: change in λn , does it change apparent color?
MC17: what changes when light enters glass?
1: travel time through piece of glass