Properties of Waves

Since the waves move back and forth objects move up and down. Imagine riding a water wave. You move up and down because the wave is moving back and forth.

Transverse Waves

A transverse wave has alternating high points, called crests, and low points, called troughs.

Parts of a Transverse Wave

You can model compressional waves with a slinky.

As the wave moves, it looks as if the whole spring is moving toward one end.

The wave carries energy, but not matter, forward along the spring.

Longitudinal (Compressional) Waves

A compressional wave has no crests and troughs.

When you make compressional waves in a coiled spring, a compression is a region where the coils are close together.

Parts of a Compressional Wave

The coils in the region next to a compression are spread apart, or less dense. This less-dense region of a compressional wave is called a rarefaction.

Rarefaction

• A wavelength is the distance between one point on a wave and the nearest point just like it.

• For transverse waves the wavelength is the distance from crest to crest or trough to trough.

Wavelength

A wavelength in a compressional wave is the distance between two neighboring compressions or two neighboring rarefactions.

Wavelength

• The frequency of a wave is the number of wavelengths that pass a fixed point each second.

• You can find the frequency of a transverse wave by counting the number of crests or troughs that pass by a point each second.

• The unit for frequency is Hertz (Hz)• Example: If 3 waves pass a point in 3

seconds, the frequency is 1Hz.

Frequency

As frequency increases, wavelength decreases

If you move the rope up, down, and back up in 1 s, the frequency of the wave you generate is 1 Hz.

Wavelength-Frequency Relationship

The speed of a wave depends on the medium it is traveling through.

Sound waves usually travel faster in liquids and solids than they do in gases. However, light waves travel more slowly in liquid and solids than they do in gases or in empty space.

Sound waves usually travel faster in a material if the temperature of the material is increased.

Speed Depends on the Medium

You can calculate the speed of a wave represented by v by multiplying its frequency times its wavelength.

Speed (m/s) = frequency (Hz) x wavelength (m)

V = f x λ

Calculating the Speed of a Wave

What is the speed of a wave with a frequency of 5 Hz that has a wavelength of 2m?

V=f x λ V= 5 x 2 = 10m/s

Example Problem 1

Example Problem 2

What is the frequency of a wave that has a wavelength of 2m and a speed of 12m/s?

V = f x λ 12 = f x 2 f = 6 Hz

Wavelength and frequency vary inversely. What does this mean?

If the wavelength is long, then the frequency is low.

If the wavelength is short, then the frequency is high.

Wavelength, Frequency & Energy

Wavelength and frequency vary inversely. What does this mean?

If the wavelength is long, then the frequency is low. If the wavelength is short, then the frequency is

high. Look at your reference table, find the

electromagnetic spectrum. Which type of electromagnetic wave has the highest

frequency?

Wavelength, Frequency & Energy

The higher the frequency the more energy the wave has.

Using your reference table, determine which wave on the electromagnetic spectrum has the least amount of energy? Hint: Which has the lowest frequency?

Wavelength, Frequency & Energy

Amplitude is related to the energy carried by a wave.

The greater the wave’s amplitude is, the more energy the wave carries.

Amplitude is measured differently for compressional and transverse waves.

The amplitude of a compressional wave is related to how tightly the medium is pushed together at the compressions.

Amplitude & Energy

Amplitude & Energy

The amplitude of any transverse wave is the distance from the crest or trough of the wave to the rest position of the medium.

Amplitude of Transverse Waves