Chapter 11 – Waves Section 1 – Types of Waves

A wave is a disturbance that carries energy through matter and space.

The matter through which a wave travels is called the medium.

The medium for a sound wave is air and the medium for an earthquake is earth. Seismic Waves Sound Wave

Waves that require a medium are called mechanical waves Waves that require a medium are called mechanical waves. Almost all waves are mechanical waves with one important exception: electromagnetic waves.

Waves carry energy. The bigger the wave, the more energy the wave carries.

Waves are related to vibrations Waves are related to vibrations. Most waves are caused by a vibrating object. In a mechanical wave, the particles of the medium vibrate as the wave passes through the medium.

A transverse wave is a wave which causes the particles of the medium to vibrate perpendicularly to the direction the wave travels.

A longitudinal wave is a wave that causes the particles of the medium to vibrate parallel to the direction the wave travels.

Chapter 10 – Waves Section 2 – Characteristics of Waves

All transverse waves are sine waves All transverse waves are sine waves. Sine waves look like a letter S place on its side.

The highest points of a transverse wave are called crests The highest points of a transverse wave are called crests. The lowest points are called troughs.

The amplitude of a wave tells you how much energy the wave has The amplitude of a wave tells you how much energy the wave has. It is measured from the top of the peak or bottom of the trough to the middle of the wave.

In a longitudinal wave, there are areas which are compressed and areas which are stretched apart. The compressed areas are called compressions and the stretched areas are called rarefactions.

Parts of a Longitudinal Wave

The distance from one crest of wave to the next crest, or from one trough to the next trough, is called wavelength. The symbol for wavelength is λ and the SI unit is meters (m).

Wavelength for a Transverse Wave

In a longitudinal wave the distance, the wavelength is the distance between two compressions or two rarefactions.

The time required for one full wavelength of a wave to pass a certain point is called the period of the wave. The period is represented by the symbol T and it is expressed in the SI unit seconds.

Period of a Transverse Wave

The frequency of a wave is the number of full wavelengths (cycles) which pass a point in 1 second. The symbol for frequency is f and the SI unit for measuring frequency is the hertz (Hz).

Frequency of a Transverse Wave

The frequency (f) and wavelength of a wave are inversely proportionate. As the frequency increases, the wavelength decreases. As the frequency decreases, the wavelength increases.

The frequency and period of a wave are related The frequency and period of a wave are related. If more waves are made per second, each one takes a shorter amount of time. In other words, the frequency is the inverse of the period. Frequency = f =

Wave Speed The speed of a wave is simply how fast a wave moves in a certain amount of time. The unit for the velocity or speed of a wave is m/s.

calculated by multiplying the wavelength (λ) by the frequency (f). The speed of a wave can be calculated by multiplying the wavelength (λ) by the frequency (f). v = f X λ v = V V f f λ T

The average wavelength in a series of ocean waves is 15 m The average wavelength in a series of ocean waves is 15 m. The frequency of the ocean waves is 0.1 Hz. What is the speed of the ocean waves?

known to be 350 m/s, what is the wavelength of this note? The musical note A above middle C has a frequency of 440 Hz. If the speed of sound is known to be 350 m/s, what is the wavelength of this note? v = f X λ

A buoy bobs up and down in the ocean. The waves have a wavelength of 2 A buoy bobs up and down in the ocean. The waves have a wavelength of 2.5 m, and they pass the buoy at a speed of 5.0 m/s. What is the frequency of the waves? v = f X λ

The speed of a wave depends on the medium. In the same medium, waves will always travel at the same speed.

The close the particles in a medium the faster the wave speed. The arrangement of particles in a medium is responsible for the differences in wave speed. The close the particles in a medium the faster the wave speed. Wave Speed follows the following trend: Solids Liquids Gases

Chapter 10, Section 3 – Wave Interactions

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

Waves which reflect from a boundary which is free to move are exactly like the original wave.

Waves reflected from a fixed boundary are turned upside down or reversed from the original wave.

The bending of waves as they pass an edge is called diffraction. Waves bend when they pass the edge of an obstacle.

When waves pass through an opening (slit), the waves will bend around both edges of the opening.

Sometimes waves are bent by refraction Sometimes waves are bent by refraction. Refraction is the bending of waves when they pass from one medium to another.

Refraction of a Wave

When several waves are in the same location, the waves combine to produce a single, new wave that is different from the original waves. This is called wave interference.

Once the waves have passed through each other and moved on, they return to their original shape.

In constructive interference the two waves, combine to form a larger wave. This wave’s amplitude is the sum of the amplitudes of the two individual waves.

Constructive Wave Interference

When the crest of one wave meets the trough of another wave, the resulting wave has an amplitude which is smaller than of the two original waves. This is called destructive interference.

Destructive Wave Interference

If reflected waves have the same amplitude, frequency, and speed as the original waves then standing waves are formed. Standing waves do not move through the medium. Instead, the waves cause the medium to vibrate in a loop or series of loops.

Standing Wave

Each loop of a standing wave is separated from the next loop by points that have no vibration called nodes. Nodes lie at points where the crests of the original waves meet the troughs of the reflected waves, causing complete destructive interference.

Midway between the nodes lie points of maximum vibration, called antinodes. Antinodes form where the crests of the original waves line up with the crests of the reflected waves so that complete constructive Interference occurs.