Chapter 21

Who first introduced the concept of electromagnetism?

André-Marie Ampère

Describe the waves in both the electric and magnetic fields as an electromagnetic wave moves.

The waves in the electric and magnetic fields are both transverse waves. They are interconnected so that they both reach their minimum and maximum values at the same time. The waves are perpendicular to each other.

Do electromagnetic waves move instantaneously?

No. They move at an extremely fast but finite speed—the speed of light.

Radio waves have longer wavelengths than x-rays. Which ones have more energy?

X-rays have more energy. Wavelength and frequency are inversely related, while frequency and energy are directly related. Therefore, wavelength and energy are also inversely related. So shorter wavelength x-rays have more energy.

The observation that specific frequencies of light have enough energy to eject electrons from metal supports the particle model of light. What do scientists call this behavior?

the photoelectric effect

Define photon.

A massless particle of electromagnetic energy—a bundle of electromagnetic energy.

Why can electromagnetic waves move through space?

Electromagnetic waves are disruptions in an electromagnetic field. Therefore, they do not need a physical medium through which to travel.

Compare mechanical and electromagnetic waves.

Both are produced by a vibrating object. Mechanical waves require a physical medium to move through, while electromagnetic waves can move through a vacuum because of the presence of an electromagnetic field. (pp. 488–89)

Explain how an electromagnetic wave is produced.

Electromagnetic waves are produced by vibrating electrons. The acceleration of the electrons produces a changing electric field and a changing magnetic field. The interaction between these two changing fields moves energy away from the source.

Thomas Young’s experiment supported which theory of light? Explain.

Young’s experiment supported the wave model of light. His experiment showed that light exhibited wave interference.

Explain what is meant by wave-particle duality.

Light exists as particles called photons. Photons are massless wave bundles of electromagnetic energy. Therefore, light is both a wave and a particle.

Name the band of electromagnetic waves that has the highest energy and the one with the lowest energy.

gamma rays and radio waves

List the seven major bands in the electromagnetic spectrum in order from shortest to longest wavelength.

gamma rays, x-rays, ultraviolet waves, visible light, infrared waves, microwaves, radio waves

What types of electromagnetic waves do cellphones use?

Cell phones use radio waves to transmit voice and data. They also use high-frequency radio waves (Bluetooth). Some students may also mention visible light for the camera.

What does infrared mean?

“below red,” indicating that the electromagnetic waves of infrared light have less energy than red light does.

What makes visible light special?

Visible light is a small part of the electromagnetic spectrum. It is special because it includes the wavelengths and frequencies that our eyes can sense. God designed our eye and visible light so that they would work together.

What type of light is considered to be just beyond the visible light portion of the electromagnetic spectrum?

Ultraviolet is just beyond visible light, having higher energy than violet (visible) light.

Compare AM and FM waves.

AM and FM waves are both types of radio waves. AM waves have a lower frequency (lower energy) and longer wavelength. AM waves are produced by changing the amplitude of the wave, while FM waves are produced by modulating the frequency.

What does a radio antenna do?

At a radio station, an antenna converts an electrical signal into a radio wave. At a receiver, the antenna converts the radio wave back into an electrical signal.