PROPERTIES OF WAVESLet’s Surf!

What is a wave?• A wave is an oscillation that travels, moving energy from one place to another

• Caused by a vibration• The oscillation spreads outward from where it started.

Properties of a Wave• A crest is the highest point of the wave.

• A trough is the lowest point of the wave.

Properties of a Wave

•The amplitude, A, of a wave is the maximum height the wave rises above the origin (equilibrium point).

Properties of a Wave

•The wave period, P, is the time it takes one wave to pass the observer.

Properties of a Wave• Wavelength is the distance from any point on a wave to the same point on the next cycle of the wave (usually from crest to crest).

• Symbol: l Units: meters (m)

Properties of a Wave•The frequency of a wave is the number of waves passing a particular point in one second.

• Symbol: ƒ Unit: Hertz (Hz) or s-1

Speed of a Wave• The speed is the distance traveled (one wavelength) divided by the time it takes (one period).

Speed = frequency X wavelength

v = ƒ·l

Example Calculations:

The wavelength of a wave on a string is 1.5 meters and its speed is 5 m/s.

Calculate the frequency.

Review Problems1. What is the speed of a wave with a frequency of 22 Hz and a wavelength of 6.2 m?

2. Calculate the frequency of a wave traveling at 3.0 x108 m/s with a wavelength of 1.96 x 10-6 m.

Relationship between frequency, wavelength and energy:• There is an inverse relationship between wavelength and frequency.

• There is a direct relationship between energy and frequency.

• Therefore:• As wavelength increases, both the frequency and energy of the wave decrease.

• As wavelength decreases, both the frequency and energy of the wave increases.

Types of Waves: Transverse• A wave whose oscillations are perpendicular to the direction the wave travels.

• Examples: Water waves, light waves, S-waves

Types of Waves: Longitudinal • A wave whose oscillations are in the same direction as the wave travels.

• aka = compression waves• Examples: Sound waves, P-waves

Standing Waves:

• A wave trapped in one spot.

• Ex. Guitar string

Four wave interactions

• When a wave encounters a surface, four interactions can occur:

1. reflection2. refraction 3. diffraction4. absorption

Examples of Interactions:1. Reflection:

• Mirror (light), echo (sound)

2. Refraction:• Eyeglasses, microscope lenses

3. Diffraction:• Hologram, prism

4. Absorption:• Sunglasses absorbing UV radiation• Sound proofing a recording studio

We see colors due to both absorption and reflection!

Constructive Interference:• Constructive interference happens when waves add up to make a larger amplitude.

• Suppose you make two wave pulses on a stretched string.

• One comes from the left and the other comes from the right.

• When the waves meet, they combine to make a single large pulse.

Destructive Inference•During destructive interference, waves add up to make a wave with smaller or zero amplitude.

•What happens when one pulse is on top of the string and the other is on the bottom?

•When the pulses meet in the middle, they cancel each other out.