Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.
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Transcript of Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.
![Page 1: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/1.jpg)
Electromagnetic Waves
AP Physics
Optics Lecture 1: Ch 22
![Page 2: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/2.jpg)
Production of Electromagnetic Waves
Since a changing electric field produces a magnetic field, and a changing magnetic field produces an electric field, once sinusoidal fields are created they can propagate on their own.
These propagating fields are called electromagnetic waves.
![Page 3: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/3.jpg)
Production of Electromagnetic Waves
Oscillating charges will produce electromagnetic waves:
![Page 4: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/4.jpg)
Production of Electromagnetic Waves
Far from the source, the waves are plane waves:
![Page 5: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/5.jpg)
Production of Electromagnetic Waves
The electric and magnetic waves are perpendicular to each other, and to the direction of propagation.
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35
![Page 6: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/6.jpg)
Propagation Speed
When Maxwell calculated the speed of propagation of electromagnetic waves, he found:
This is the speed of light in a vacuum.
2
0 0
1c
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Light was known to be a wave; after producing electromagnetic waves of other frequencies, it was known to be an electromagnetic wave as well.
The frequency of an electromagnetic wave is related to its wavelength:
Light as an EM Wave
![Page 8: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/8.jpg)
Electromagnetic waves can have any wavelength; we have given different names to different parts of the wavelength spectrum.
Light as an EM Wave
![Page 9: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/9.jpg)
Measuring the Speed of Light
The speed of light was known to be very large.
Newton tried to measure it with pendulums as a timing device.
1676: Romer was measuring the orbital periods of Io, a moon of Jupiter
![Page 10: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/10.jpg)
Speed of Light
Experiments by Fizeau
![Page 11: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/11.jpg)
Measuring the Speed of Light
One important measurement, by Michelson, used a rotating mirror:
![Page 12: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/12.jpg)
Measuring the Speed of Light
Over the years, measurements have become more and more precise; now the speed of light is defined to be:
This is then used to define the meter.
![Page 13: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/13.jpg)
22.5 Energy in EM Waves
Energy is stored in both electric and magnetic fields, giving the total energy density of an electromagnetic wave:
Each field contributes half the total energy density.
![Page 14: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/14.jpg)
Energy in EM Waves
This energy is transported by the wave.
![Page 15: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/15.jpg)
Radiation Pressure
In addition to carrying energy, electromagnetic waves also carry momentum. This means that a force will be exerted by the wave.
The radiation pressure is related to the average intensity. It is a minimum if the wave is fully absorbed:
And a maximum if it is fully reflected:
![Page 16: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/16.jpg)
22.7 Radio and Television; Wireless Communication
The mixing of signal and carrier can be done two ways. First, by using the signal to modify the amplitude of the carrier (AM):
![Page 17: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/17.jpg)
22.7 Radio and Television; Wireless Communication
Second, by using the signal to modify the frequency of the carrier (FM):
![Page 18: Electromagnetic Waves AP Physics Optics Lecture 1: Ch 22.](https://reader035.fdocuments.us/reader035/viewer/2022081721/56649f465503460f94c68c55/html5/thumbnails/18.jpg)
Radio and Television; Wireless Communication
At the receiving end, the wave is received, demodulated, amplified, and sent to a loudspeaker: