Recall from Magnetism:
1. An ocean wave traveling at 3 m/s has a wavelength of 1.6 meters. a. What is the frequency of the wave?
Electromagnetic Induction
A moving charged particle creates a magnetic field perpendicular to the moving charges.
A changing magnetic field creates a potential difference perpendicular to the magnetic field.
b. What is the period of the wave?
Electromagnetic (Light) Waves
Electromagnetic Waves
1
Visible light, infrared light, xrays, microwaves, gamma rays, etc. are all part of the electromagnetic Electromagnetic waves all travel at the same speed in a vacuum
spectrum. They all travel with the same _____________ in a vacuum. However, they have different
__________________ (Hz) and ___________________ (m). Find the spectrum in your reference table.
Monochromatic
2. What type of EM wave is the following?
Electromagnetic waves are transverse waves. 500,000 hertz _________________________
Radio waves travel from New York City to the antenna on your radio in Hicksville.
5.0 x 109 meter_________________________
How should you orient the antenna on your radio to get reception, horizontally or vertically? Why?
3.0 x 1013 hertz _________________________
4.5 x 1014 hertz _________________________
200 meters _________________________
3. What is the frequency of a 632 nanometer EM wave? What color is it?
4. What is the wavelength of a 5 x 1013 Hz EM wave? What type of wave is it?
5. The antenna of a device is (approximately) the wavelength of the incoming signal. If you’re purchasing a home phone and want one with a smaller antenna, which should you buy, a 900 Mhz or a 2.4 Ghz phone? Why?
Doppler effect 6. How long should you make an antenna to pick up an AM radio signal of 800 khz?
Light from a star in distance space is expected to have a frequency of 6.3 x 1014 Hz. Instead the star has a slightly lower frequency than what would have been expected. Is the star moving towards or away from Earth? Is this a red shift or blue shift?
2
Speed of an electromagnetic waves (light) in a medium
9. Light with a frequency of 5.2 x 1015 Hz is traveling through water. a. How fast is it traveling?
When light enters a new medium, the speed changes and the wavelength changes but the frequency remains the same. For all wave phenomena, frequency always remains the same except for the Doppler Effect.
b. What is the wavelength of the light in water?
7. What is the speed of light in:
10. Light with a frequency of 3.84 x 1014 Hz is traveling through glycerol. a. Corn oil
a. How fast is it traveling?
b. Diamond
b. What is the wavelength of the light in glycerol?
c. Water
8. Light travels at 1.563 x 108 m/s through a material. What is the composition of the material?
Energy of an electromagnetic wave (light)
Higher frequency EM waves have higher energy
Ephoton = (found in the Modern Physics part of the reference table)
Phase (True for all waves, not just EM waves)
A photon is the smallest particle of light – like an atom is the smallest particle of matter. 2 points are in phase if they are on the same part of a wave
9. An electromagnetic wave has a frequency of 5.1 x 1014 Hz
2 points are 180 degrees out of phase at opposite parts
a. What color wave is this?
In Phase
Out of Phase
b. What is the energy of the wave?
c. What is the speed of this wave in a vacuum?
10. A photon is traveling with a frequency of 8.6 x 1016 Hz
a. What type of EM wave is this?
b. How much energy does this photon have?
c. What is the wavelength of this wave?
11. An electromagnetic wave is traveling with frequency 3 x 107 Hz
a. What type of EM wave is this?
b. How much energy does it have?
c. What is the speed of this wave in a vacuum?
Reflection
Polarization
A polarizing filter blocks out all waves except those with particles moving in a certain direction.
Law of reflection:
12. To the right (using a protractor and ruler)
This only works for transverse waves a. Draw the normal
– longitudinal waves can NOT be polarized.
b. What is the angle of incidence?
c. What is the angle of reflection?
d. Draw the reflected ray.
3
Diffraction Electromagnetic waves diffract just like mechanical waves 13. To the right (using a protractor and ruler)
There is no change in medium necessary for diffraction
An incident ray has an angle of 20 degrees
14. A 7x1014 Hz EM wave in air goes through a hole and diffracts
a. Draw the incident ray (and normal)
a. What is the speed before it goes through the opening?
b. Draw the reflected ray
b. What is the speed after?
c. What is the wavelength before the opening?
d. What is the wavelength after? e. Sketch four diffracted wave fronts after the opening
Note: Larger wavelength and smaller opening > More diffraction
15. Radio waves and light waves go past tall buildings. Which will diffract more? Why?
Interference Electromagnetic waves interfere just like mechanical waves
Mechanical waves vs Electromagnetic waves
If you put a paper to observe light
along BDC, what would the pattern Can travel in a vacuum
look like?
Transverse or longitudinal
Energy is related to
Requires a medium to travel
Tastes good on a pizza
Refraction (transmission when light enters a new medium)
When light (EM waves) enter a different medium, there is a change in ____________________ 16. A ray of light (f=5.09 x 1014 Hz) is incident on the boundary which causes a change in __________________ or ______________________
between air and an unknown material X at an angle of incidence of 55°, as shown. The absolute index of refraction of material X is 1.66.
Recall: as light travels through a different medium, its speed changes according to the index of refraction
a. Determine the speed of light in material X
n = b. Calculate the angle of refraction of this light ray
Light changes direction (angle) according to Snell’s Law
4
17. A monochromatic light ray (f=5.09 x 1014 Hz) traveling in air is incident on the surface of a rectangular block of Lucite (n=1.50).
a. Measure the angle of incidence for the light ray to the nearest degree
18. A ray of monochromatic light having a frequency of 5.09 × 1014 hertz is incident on an interface of air and corn oil at an angle of 35° as shown. The ray is transmitted through parallel layers of corn oil and glycerol and is then reflected from the surface of a plane mirror, located below and parallel to the glycerol layer. The ray then emerges from the corn oil back into the air at point P.
b. Calculate the angle of refraction of the light ray when it enters the Lucite block.
a. Calculate the angle of refraction of the light ray as it enters the corn oil from air.
c. What is the angle of refraction of the light ray as it emerges from the Lucite block back into the air?
b. Explain why the ray does not bend at the corn oilglycerol interface.
c. On the diagram, use a protractor and straightedge to construct the refracted ray representing the light emerging at point P into the air.
Why is the sky blue?
Dispersion
Why do all refraction problems specify the same frequency (f=5.09 × 10 hertz)?
14
Why is the sun yellow?
Why are sunsets red?
20. Orange light has a frequency of 5.0 x 1014 Hz in a vacuum. What is the wavelength of this light?
6 x 107m
21. How much time does it take light from the moon to reach Earth?
19. A wave generator with a constant frequency produces parallel wave fronts in a tank of water of two different depths. The diagram below represents the wave fronts in the deep water. As the wave fronts travel from the deep water into the shallow water, the speed of the waves decreases. On the diagram at right use a straightedge to draw at least three lines to represent the wave fronts, with appropriate spacing, in the shallow water.
How much time would it take a radio wave to travel from the moon to Earth?
1.28 sec for both
22. What is the energy in Joules of a photon with wavelength 532 nm? 3.7 x 1019 J
23. A hydrogen atom emits a photon with an energy of 1.63 x 1018 J. What type of radiation would this photon be classified? (i.e. infrared, blue light, xray, etc.)
f = 2.46 x 1015 Hz > Ultraviolet
24. Radio waves diffract around buildings more than light waves do because compared to light waves, radio waves (move faster) (move slower) (have a higher frequency) (have a longer wavelength)
Longer wavelength
25. A ray of monochromatic light (f = 5.09 x 1014 hertz) in air is incident at an angle of 30° on a boundary with corn oil. What is the angle of refraction?
19.9 degrees
26. A monochromatic ray of light (f = 5.09 x 1014 hertz) traveling in air is incident upon medium A at an angle of 45°. If the angle of refraction is 29°, what is medium A? (water, fused quartz, Lucite, or flint glass)
n = 1.46 fused quartz
27. A ray of light is travelling from water to diamond. If the incident angle is 45°, what will the angle of refraction be?
22.9 degrees
5