Chapter 23Chapter 23

Characteristics of WavesCharacteristics of Waves

23-1 Nature of Waves

• Ocean waves don’t flood the beach because they don’t carry water—they only move it up and down, not forward.

• Waves are formed along the surface of the water as the result of a disturbance.

• Waves carry energy.• A wave is a traveling disturbance that

carries energy from one place to another.• Waves get their energy from vibrations

caused by something that is moving.• Electric charges can vibrate to create light

and microwaves.

• The matter that energy travels through is called a medium.

• Mechanical waves require a medium to carry energy while electromagnetic waves do not.

• Mechanical wave = sound • Electromagnetic = light.

23-2 Characteristics of Waves

• All waves have amplitude, wavelength, and frequency.

• The highest point of a wave is the crest.

• The lowest point of a wave is the trough.

Amplitude

• A wave’s maximum movement from rest is called amplitude.

• It’s the distance from rest to the crest or trough.

• The higher the amplitude the greater the energy.

Wavelength

• The wavelength is the distance from crest to crest or trough to trough.

• Longer wavelengths have less energy than short ones.

• The symbol for wavelength is the Greek symbol lambda λ.

Frequency

• The number of complete waves per unit of time is frequency. It is usually measured in waves per second.

• The unit used to measure frequency is the hertz (Hz).

23-3 Types of Waves

• Depending on the motion of the medium as compared to the movement of the wave, waves are classified as either transverse or longitudinal.

Transverse Waves

• Transverse waves are the same type as a wave on a rope.

• A wave in which the motion of the medium is at right angles to the direction of the wave is called a transverse wave.

• Light and other electromagnetic waves are transverse waves.

Longitudinal Waves

• Longitudinal waves have a series of compacted particles (compression) and spaces of uncompacted particles (rarefaction).

• The motion of the medium is parallel to the direction of the wave.

• These waves move like a slinky.

Combinations of Waves

• Some waves are a combination of transverse and longitudinal waves.

• An example is a surface wave which occur at the surface between the two mediums.

• Water waves are surface waves because they travel between water and air. The particles move up and down and back and forth.

23-4 Speed of Waves

• The speed of a wave depends on the number of waves passing a point in a certain amount of time.

• Speed = frequency x wavelength• Speed = f x λ

• In a given medium, the speed of a wave is constant. • The speed of a wave depends upon the medium

through which it is traveling.• The more dense a medium is, the slower the wave

will travel through it because the denser medium has more inertia.

• A wave moves faster through a medium that is elastic. Elasticity is the ability of the medium to return quickly to its original shape after being disturbed.

23-5 Interactions of Waves

• When a wave is traveling through a medium and hits a different medium, like air to water, it will either be reflected, refracted, diffracted or encounter interference.

Reflection

• If a wave hits a barrier, at least part of it will bounce back. This is reflection.

• The law of reflection states that the angle of incidence (i) is equal to the angle of reflection (r).

• Looking in the mirror is an example of light waves reflecting back with your image.

Refraction

• When waves go from one medium to another and the speed of the wave changes, the waves will bend as they either speed up or slow down. This is refraction.

Bent looking straw due to refraction

Diffraction

• The bending of waves around the edge of an obstacle is diffraction.

• The amount of diffraction depends on the wavelength and the size of the obstacle.

Interference

• When two or more waves arrive at the same place at the same time, that’s interference.

• There are two kinds: constructive and destructive.

Constructive Interference

• Constructive interference occurs when waves with different amplitudes line up together—crests and troughs.

• The crests of the two waves add together to form a single wave with an amplitude equal to the sum of the amplitudes of the two original waves.

Destructive Interference

• With destructive interference, the crests don’t line up and the amplitudes subtract one another out.

• If the crest of one wave occurs at the trough of another wave, they will cancel one another out with no wave at all.

Standing Waves

• If a wave vibrates at just the right frequency, it will appear to stop moving and create a standing wave.

Standing Waves

• Standing waves result when an object vibrates at its resonant frequency and multiples of that frequency. The top wave has two nodes and one antinode. What about the others?

Resonance

• An object that is vibrating at its natural frequency can cause another object to vibrate by absorbing energy of its own natural frequency. This is called resonance. Tacoma Narrows Bridge

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