Key Concepts
How are electromagnetic waves different from mechanical waves?
What is the maximum speed of light?
How do electromagnetic waves differ from one another?
What is the dual nature of electromagnetic radiation?
What happens as light travels farther from its source?
Vocabulary
electromagnetic waves
electric field
magnetic field
electromagnetic radiation
photoelectric effect
photons
intensity
Reading Strategy
Comparing and Contrasting Copy the table below. As you read about electromagnetic waves, fill in the table to compare them with mechanical waves. Use E for properties of electromagnetic waves, M for mechanical waves, and B for both.
Travels through vacuum |
E |
Travels through medium |
a. |
Fits wave model |
B |
Fits particle model |
b. |
Transverse wave |
c. |
Longitudinal wave |
d. |
What do X-ray machines, microwave ovens, and heat lamps have in common with police radar, television, and radiation therapy? They all use waves. You are surrounded by such waves all the time. But you may not realize it, because most waves are invisible.
With X-rays, you can take pictures of your bones. Your dentist uses X-rays to examine the inner structure of your teeth. Microwaves cook or reheat your meals and carry cell phone conversations between you and your friends. Radio waves bring your favorite music to your radio from the radio station. Ultraviolet rays can give you a sunburn. Without waves, the girl in Figure 1 wouldn't be able to talk with her friends on a cell phone. Without waves, you wouldn't be able to watch your favorite TV show. You wouldn't be able to see colors. In fact, without waves you wouldn't be able to see any-thing at all.
Figure 1 The waves that carry this girl's cell phone conversation are not visible. The girl may not even know they exist. But their existence is what makes cell phone technology possible.