22.1 - Light and electromagnetism

When you look at sunlight streaming in through the window you probably don’t associate the light with mental images of electricity or magnets. You probably don’t think of atoms either. The nature of light was a mystery for thousands of years until physicists of the late 19th century discovered the connection among light, electricity, and magnetism. In the early 20th century physicists went further, connecting the emission and absorption lines of light to the properties of the atom (Chapter 26). Read the text aloud
Light and the oscillating electric field
In 1865, physicist James Clerk Maxwell developed a theory of electricity and magnetism that predicted the existence of traveling waves. He calculated the speed of these waves and found that it matched the speed of light. Based on this evidence, Maxwell made a strong argument that light was a form of electricity and magnetism. Just 24 years later, in 1889, Heinrich Hertz proved experimentally the existence of Maxwell’s electromagnetic waves and demonstrated conclusively that these waves had all the properties of light. Read the text aloud Show Who was James Maxwell?
Consider a stationary positive charge. The charge creates an electric field satisfying Coulomb’s law that reaches out in every direction and affects other charges. A negative charge nearby feels the electric force of attraction from the positive charge. Maxwell asked the following question: How fast does the force get from one charge to the other? Read the text aloud
An oscillating electric charge creates an electromagnetic wave
In Chapter 18 we considered the electric field of static charges. Now, consider a positive charge that oscillates up and down. The charge’s motion creates a corresponding wiggle, or wave, in the electric field! That wave travels at the speed of light and causes distant charges to respond. An oscillating charge creates a traveling oscillation in the electromagnetic field that travels outward at the speed of light. Read the text aloud
Light is a traveling oscillation of the electromagnetic field. In the previous chapter we learned that a moving electric charge (current) creates a magnetic field. Therefore, the oscillating positive electric charge in the above example creates an oscillating magnetic field as well as an electric field. Once started, the electric field generates a magnetic field as it changes. The magnetic field in turn generates an electric field as it changes. The electric and magnetic fields propagate with each other in an electromagnetic wave. Read the text aloud
Light is made up of a combination of what two oscillating fields?
  1. electric and magnetic
  2. magnetic and gravitational
  3. electric and gravitational
  4. soccer and baseball
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