Section 1: Types of Waves

Section 2: Characteristic of Waves

Section 3: Wave Interactions

Section 1: Types of Waves KEY TERMS

Wave

Medium

Mechanical Wave

Electromagnetic Wave

Transverse Wave

Longitudinal Wave

Section 1: Types of Waves What Is a Wave?

Is a disturbance that carries energy through matter or space. A wave is not just the movement of matter from one place to another.

Section 1: Types of Waves Most waves travel through a Medium

So what is a medium?

A medium is the matter through which a wave travels.

Examples: Sound Waves – Air

Seismic Waves – Earth

All wave that require a medium are called mechanical waves.

Section 1: Types of Waves Light does not require a medium

Light waves consist of changing electric and magnetic fields in space.

Light waves are called electromagnetic waves. Light and light waves may refer to any electromagnetic wave not just visible light.

Section 1: Types of Waves Waves transfer energy

Energy is the ability to exert a force over a certain distance. It is also the ability to do work.

How do we know that waves carry energy?

Section 1: Types of Waves Energy may spread out as a wave travels

A wave front has the same amount of total energy but is spread out over a larger area.

Section 1: Types of Waves Vibrations and Waves

Waves are related to vibrations. Most waves are caused by a vibrating object.

Electromagnetic – Vibrating charged particles

Mechanical – Vibrating particles in a medium

Section 1: Types of Waves Vibrations involve transformation of energy

Figure 4 Page 457

When a mass hanging on a spring is disturbed from rest, it starts to vibrate up and down around its original position.

Section 1: Types of Waves Changing from elastic potential energy to kinetic energy

and back to elastic and gravitational potential energy.

A mass bouncing up and down cause a vibration called simple harmonic motion.

Section 1: Types of Waves A wave can pass through a series of vibrating objects

As energy is transferred from the first object to the second object the first object slows down.

A vibration that fades out is called damped harmonic motion.

The motion of particles in a medium is like the motion of masses on springs.

Section 1: Types of Waves Transverse and Longitudinal Waves Particles in a medium can vibrate either up and down or

back and forth. How are waves classified? By the direction that the particles move in the medium as

the wave passes.

Section 1: Types of Waves Transverse waves have perpendicular motion

Waves in which the motion of the particles is perpendicular to the motion of the wave as a whole are called Transverse waves.

Example – Light waves

Section 1: Types of Waves Longitudinal waves have parallel motion

Waves that cause the particles in a medium to vibrate parallel to the direction of the wave motion are called longitudinal waves.

Example – Sound waves

Section 1: Types of Waves In a surface wave, particles move in circles

Surface waves occur at the boundary between two different mediums, such as water and light.

Surface wave particles have both perpendicular and parallel motion in relation to the wave motion.

Section 2: Characteristic of Waves KEY TERMS

Crest

Trough

Amplitude

Wavelength (λ)

Period

Frequency

Doppler Effect

Section 2: Characteristic of Waves

Wave Properties

An ideal transverse wave has the shape of a sine

curve.

A sine curve looks like an S lying on its side. A wave with this shape is referred to as a sine wave.

Section 2: Characteristic of Waves Amplitude measures the amount of particle

vibration

Highest point on a transverse wave is the crest

Lowest point on a transverse wave is the trough

The greatest distance that particles are displaced from their normal resting positions because of a wave is called amplitude.

Section 2: Characteristic of Waves Amplitude is also half the distance between the crest

and trough .

Large waves have larger amplitudes and carry more energy

Longitudinal waves do not have crest and troughs because they cause particles to move back and forth instead of up and down.

Section 2: Characteristic of Waves Crowded areas of a longitudinal wave is called

compressions an the stretched-out areas are called rarefractions

Wavelength measures the distance between two equivalent parts of a wave

The distance from one crest to the next crest, or from one trough to the next trough is called the wavelength.

Section 2: Characteristic of Waves For longitudinal waves, the wavelength is between two

compressions or two rarefractions.

Not all waves have a single wavelength that is easily measured.

If the source of a wave vibrates in an irregular way, the wave length may change over time.

Wavelength is represented by the Greek Letter Lambda (λ) and is measured in meters.

Section 2: Characteristic of Waves

The period measures how long it takes for waves to pass by

The period is a also the time required for one complete vibration of a particle in a medium

In an equation the period is represented by a (T) because period is a measure of time (seconds).

Section 2: Characteristic of Waves Frequency measures the rate of vibrations

The frequency of a wave is the number of full wavelengths that pass a point in a given time interval. It also measures how rapidly vibrations occur in the medium, at the source of the wave or, both.

Frequency (f) is measured in Hertz (Hz) and named for Heinrich Hertz

Section 2: Characteristic of Waves Heinrich Hertz became the first person to

experimentally demonstrate the existence of electromagnetic waves in 1888.

The frequency and period of a wave are related.

The more vibrations in a second the shorter the amount of time .

Section 2: Characteristic of Waves Frequency is the inverse of the period.

Frequency-Period Equation

Section 2: Characteristic of Waves Light comes in a wide range of frequencies and

wavelengths

We detect light with a frequency from about

4.3 χ 10¹⁴ Hz to 7.5 χ 10¹⁴ Hz. This is visible light

What accounts for the different colors we see?

Difference in frequencies

The full range of light at different frequencies and wavelengths is called the electromagnetic spectrum

Section 2: Characteristic of Waves

Wave Speed

Wave speed equals frequency times wavelength

Section 2: Characteristic of Waves Wave speed is simply how fast is a wave moving

For a wave we use wavelength (λ) as our distance and the period as our time.

Section 2: Characteristic of Waves Because the period is the inverse of the frequency,

dividing by the period is equivalent to multiplying by the frequency

Wave Speed Equation

wave speed = frequency χ wavelength

v = f χ λ

Section 2: Characteristic of Waves Solving for frequency

Section 2: Characteristic of Waves The speed of a wave depends on the medium

Sound travels in air at a rate of 340m/s

In water it is 3 to 4 times faster and in a solid it is 15 to 20 times faster.

In a given medium, the speed of the wave is constant, it does not depend on the frequency of the wave.

Section 2: Characteristic of Waves

Kinetic theory explains differences in wave speed

What determines how well a wave will travel in a medium?

The arrangement of particles

Gases – waves do not travel well because of the empty space

Section 2: Characteristic of Waves

Liquids – vibrations are transferred quickly from one molecule to the next. Waves are able to travel faster in liquid than in gases.

Solids – Molecules are close together and in a fixed position. As a result, waves travel very quickly through most solids.

Section 2: Characteristic of Waves Light has a finite speed

All electromagnetic waves in empty space travel at the same speed, the speed of light 3.00 x 10⁸m/s (186,000mi/s)

Light travels slower when it passes through a medium

Section 2: Characteristic of Waves

The Doppler Effect

Pitch is determined by the frequency of sound waves.

Pitch of a sound, how high or low it is, is determined by the frequency at which the

sound waves strike the eardrum.

Section 2: Characteristic of Waves Frequency changes when the source of the wave is

moving.

A change in the observed frequency of a wave results from the motion of the source or observer is called the Doppler Effect.

Section 3: Wave Interactions Key Terms

Reflection

Diffraction

Refraction

Interference

Constructive Interference

Destructive Interference

Standing Wave

Section 3: Wave Interactions Reflection, Diffraction, and Refraction

Reflection is simply the bouncing back of a wave when it meets a surface or boundary.

Waves reflected at a free boundary

The reflected wave is exactly like the original wave except it travels in the opposite direction

Section 3: Wave Interactions At a fixed boundary, waves reflect and turn upside

down

Diffraction is the bending of waves around an edge

When waves pass the edge of an object or pass through an opening, they spread out as if a new wave was created.

Section 3: Wave Interactions Waves can also bend by refraction

Refraction is the bending of a wave front as the wave front passes between two substances in which the speed of the wave differs.

All waves are refracted when they pass from one medium to another at an angle.

Section 3: Wave Interactions Interference

More than one wave can exist in the same place at the same time.

Waves in the same place combine to produce a single wave.

Interference is the combination of two or more waves of the same frequency that result in a single wave.

Section 3: Wave Interactions Crest are positive and troughs are negative

This method of adding waves is sometimes known as the principle of superposition.

Constructive interference increases amplitude

When the crest of one wave overlaps the crest of another wave, the waves reinforce each other

Section 3: Wave Interactions Constructive interference is any interference in which

waves combine so that the resulting wave is bigger than the original wave.

Destructive interference decreases amplitude

When the crest of one wave meets the trough of another wave, the resulting wave has a smaller amplitude then the larger of the two waves.

Section 3: Wave Interactions Destructive interference is any interference in which

waves combine so that the resulting wave is smaller than the largest of the original waves.

When destructive interference occurs between two waves that have the same amplitude, the waves may completely cancel each other out.

Interference of light waves creates colorful displays

Section 3: Wave Interactions Interference of sound waves produce beats

When the compressions from two tuning forks arrive at the same time, constructive interference occurs, and the sound is louder.

When a compression and rarefraction arrive at the same time, destructive interference occurs, and the sound is softer.

The series of loud and soft sounds are called beats

Section 3: Wave Interactions Standing Waves

Interference can cause standing waves.

Standing waves can form when a wave is reflected at the boundary of a medium

The original wave is interfering with the reflected wave causing the medium to vibrate in a stationary pattern that resembles a loop or series of loops

Section 3: Wave Interactions Waves are traveling in both directions

Standing waves have nodes and antinodes

The point of separation between each loop is the node

At the node complete destructive interference occurs. No vibration occurs .

Section 3: Wave Interactions The point midway between the nodes is called an

antinode. Antinodes lay at the top or bottom of each loop.

At the antinode complete constructive interference occurs producing maximum vibration.

Standing waves can have only certain wavelengths

Section 3: Wave Interactions The simplest standing wave occurs when the

wavelength is twice the length of the string.

At a certain frequency, the wavelength is exactly equal to the length of the string producing a node in the middle of the string.

Standing waves can exist whenever a multiple of half-wavelengths will fit exactly in the length of the string.