3.5 Light and the Electromagnetic Field

Pre-Lecture Reading 3.5

Video Lecture

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Light and the Electromagnetic Field (11:07)

Supplementary Notes

Vacuum

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See Vacuum.
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Light travels as a wave.
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All waves require a medium.
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Vacuum is defined as the absence of any medium.
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Hence, vacuum cannot be the medium through which light travels.

Electromagnetic Field

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See Electromagnetic Field.
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Electromagnetic fields are analogous to gravitational fields: They emanate from charges as gravitational fields emanate from masses.
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If a charge is stationary, there are no waves in its electromagnetic field.
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If a charge moves back and forth, this motion creates a wave in its electromagnetic field.
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If other charges encounter this wave, they move back and forth in response.
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This is how radio waves are emitted and received.
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Radio waves are light. Indeed, this is how all light is emitted and received.
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Hence, light is a wave in the electromagnetic field.
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And the electromagnetic field is the medium through which light waves travel.

In both this course and Astronomy 102, we will learn about different physical processes that move charge back and forth. Each results in a different spectrum of light.

Assignment 3

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Do Question 3.