Waves UnitWaves Unit

Waves, sound and lightWaves, sound and light

Waves and VibrationsWaves and Vibrations A vibration is a A vibration is a

movement that occurs movement that occurs in a period of time.in a period of time.

A wave is a A wave is a movement that occurs movement that occurs in a period of time in a period of time and also in space.and also in space.

A wave is a way of A wave is a way of transferring energy.transferring energy.

Time for a CycleTime for a Cycle

The time that it takes The time that it takes for a wave (or for a wave (or vibration) to complete vibration) to complete one cycle is called a one cycle is called a period (T).period (T).

A cycle is when a A cycle is when a process starts to process starts to repeat itself.repeat itself.

A period is measured A period is measured in units of time in units of time (seconds, most of the (seconds, most of the time).time).

Simple Harmonic MotionSimple Harmonic Motion

The swinging of a pendulum (or a mass The swinging of a pendulum (or a mass bouncing on a spring), the motion back-and-bouncing on a spring), the motion back-and-forth, is called simple harmonic motion.forth, is called simple harmonic motion.

The result of this simple oscillation back-and-The result of this simple oscillation back-and-forth is a sine wave.forth is a sine wave.

Wave CharacteristicsWave Characteristics There are some distinct parts of a wave There are some distinct parts of a wave

called characteristics.called characteristics. The peak is the top part of the wave.The peak is the top part of the wave. The trough is the bottom part of the wave.The trough is the bottom part of the wave.

More CharacteristicsMore Characteristics

The baseline is the line of 0 energy in the wave.The baseline is the line of 0 energy in the wave. The wavelength (The wavelength ()is the distance from peak to )is the distance from peak to

peak of the wave.peak of the wave. The amplitude is the distance from the baseline The amplitude is the distance from the baseline

to the peak of the wave.to the peak of the wave.

More CharacteristicsMore Characteristics Period (T) is the time that it takes for the Period (T) is the time that it takes for the

wave to start over again, typically it is the wave to start over again, typically it is the time for one wavelength (time for one wavelength () to pass by.) to pass by.

Frequency (Frequency (ff)is the number of )is the number of to pass by to pass by in a time frame.in a time frame.

Frequency is measured in Hertz (Hz).Frequency is measured in Hertz (Hz).

Wave SpeedWave Speed

It is calculated by It is calculated by dividing distance dividing distance by time.by time.

With a wave, it is no With a wave, it is no different, we just different, we just change some of the change some of the symbolssymbols

The velocity of a The velocity of a wave is calculated by wave is calculated by dividing wavelength dividing wavelength by period of the by period of the wave.wave.

v = v = / T or / T or v = v = ff

v = d / tv = d / t

How is speed How is speed (velocity) (velocity) calculated?calculated?

Simple CalculationsSimple Calculations

What is the speed What is the speed of a wave that has of a wave that has a wavelength of a wavelength of 10.0 meters and it 10.0 meters and it takes 2.0 seconds takes 2.0 seconds to go by?to go by?

The solution is:The solution is: = 10.0 m= 10.0 m T = 2.0 sT = 2.0 s v = v = / T / T So,So, v = 10.0 m / 2.0 sv = 10.0 m / 2.0 s v = 5.0 m/sv = 5.0 m/s

What is the What is the velocity of a wave velocity of a wave that has a that has a wavelength of 5.0 wavelength of 5.0 x 10x 10-3-3 meters and a meters and a frequency of 20.0 frequency of 20.0 Hz?Hz?

The solution is:The solution is: = 5.0 x 10= 5.0 x 10-3-3 m m f = 20.0 Hzf = 20.0 Hz v = v = ff So,So, v = (5.0 x 10v = (5.0 x 10-3-3m)m)

(20.0 Hz)(20.0 Hz) v = 0.10 m/sv = 0.10 m/s

What is the What is the wavelength of a wavelength of a wave that travels wave that travels at 4.00 m/s and at 4.00 m/s and has a period of 3.0 has a period of 3.0 seconds?seconds?

The solution is:The solution is: v = 4.00 m/sv = 4.00 m/s T = 3.0 sT = 3.0 s = v T= v T So,So, = (4.00 m/s)(3.0 = (4.00 m/s)(3.0

s)s) = 12 m= 12 m

What is the What is the wavelength of a wavelength of a wave that travels wave that travels at 200.0 m/s and at 200.0 m/s and has a frequency of has a frequency of 40.0 Hz?40.0 Hz?

The solution is:The solution is: v = 200.0 m/sv = 200.0 m/s ff = 40.0 Hz = 40.0 Hz = v / = v / f f So,So, = (200.0 = (200.0

m/s)/(40.0 Hz)m/s)/(40.0 Hz) = 5.00 m= 5.00 m

What is the What is the frequency of a frequency of a pendulum if it pendulum if it swings back and swings back and forth with a period forth with a period of 4.0 seconds?of 4.0 seconds?

The solution is:The solution is: T = 4.0 sT = 4.0 s ff = 1 / T = 1 / T So,So, ff = 1 / (4.0 s) = 1 / (4.0 s) ff = 0.25 Hz = 0.25 Hz

What is the period What is the period of a wave if the of a wave if the wavelength is 20.0 wavelength is 20.0 m and the velocity m and the velocity is 10.0 m/s?is 10.0 m/s?

The solution is:The solution is: = 20.0 m= 20.0 m v = 10.0 m/sv = 10.0 m/s T = T = / v / v So,So, T = (20.0 m)/(10.0 T = (20.0 m)/(10.0

m/s)m/s) T = 2.00 sT = 2.00 s

Types of WavesTypes of Waves There are 2 basic types of waves.There are 2 basic types of waves. One is called a longitudinal wave.One is called a longitudinal wave. The other is called a transverse wave.The other is called a transverse wave.

Longitudinal WaveLongitudinal Wave Longitudinal waves move the medium parallel to Longitudinal waves move the medium parallel to

the motion of the wave.the motion of the wave. Longitudinal waves are compression waves.Longitudinal waves are compression waves. Longitudinal waves have the same Longitudinal waves have the same

characteristics as transverse waves.characteristics as transverse waves. However, peaks are referred to as condensations However, peaks are referred to as condensations

and troughs are rarefactions.and troughs are rarefactions.

Transverse WavesTransverse Waves

Transverse waves move the medium Transverse waves move the medium perpendicular to the motion of the wave.perpendicular to the motion of the wave.

Transverse waves are like ocean waves.Transverse waves are like ocean waves.

A Different Type of Transverse A Different Type of Transverse WaveWave A different type of A different type of

transverse wave is transverse wave is called the standing called the standing wave.wave.

This is a wave that This is a wave that travels back and travels back and forth between 2 forth between 2 points.points.

N is called a node N is called a node (null point).(null point).

A is called an anode A is called an anode (anti-null point).(anti-null point).

How do waves interact?How do waves interact?

When waves When waves interact, it is called interact, it is called interference.interference.

There are 2 types There are 2 types of interference.of interference.

Constructive Constructive interferenceinterference

Destructive Destructive interferenceinterference

Constructive interferenceConstructive interference

Constructive interference is when 2 or more Constructive interference is when 2 or more waves come together and build themselves waves come together and build themselves up.up.

They add their collective amplitudes They add their collective amplitudes together.together.

Destructive interferenceDestructive interference

Destructive interference is when 2 or more Destructive interference is when 2 or more waves tear each other down.waves tear each other down.

They are off by “half a phase” and their They are off by “half a phase” and their amplitudes (peak and trough) subtract from amplitudes (peak and trough) subtract from each other.each other.

What happens if the What happens if the interference keeps interference keeps

progressing?progressing? If the interference If the interference

keeps going, then it keeps going, then it is called resonance.is called resonance.

Resonance is when Resonance is when the waves keep the waves keep building upon each building upon each other.other.

This occurs with This occurs with constructive constructive interference.interference.

What happens if the source of What happens if the source of the wave is moving?the wave is moving?

If the source of the If the source of the wave is moving, then wave is moving, then the wave adjusts for the wave adjusts for the speed.the speed.

It compresses or It compresses or expands depending expands depending on the direction the on the direction the source is moving source is moving relative to the relative to the detector of the wave.detector of the wave.

Doppler Effect with SoundDoppler Effect with Sound If the object isn’t If the object isn’t

moving, then the moving, then the sound generated sound generated stays constant.stays constant.

If the object is If the object is moving toward moving toward another object, then another object, then the sound is the sound is compressed.compressed.

This gives the sound This gives the sound a higher frequency a higher frequency and a higher pitch.and a higher pitch.

If the source is If the source is moving away from moving away from the observer, then the observer, then the sound is the sound is stretched out as it stretched out as it reaches the reaches the observer.observer.

This gives the sound This gives the sound a lower frequency or a lower frequency or a lower pitch.a lower pitch.

Doppler Effect with LightDoppler Effect with Light Similarly to sound, if Similarly to sound, if

the object is not the object is not moving, then the light moving, then the light emitted is normal.emitted is normal.

If the source of the If the source of the light is moving close light is moving close to the speed of light, to the speed of light, then the light is then the light is compressed and it is compressed and it is given a higher given a higher frequency (more frequency (more energy).energy).

However, if the source However, if the source of the light is moving of the light is moving away from the away from the observer at nearly the observer at nearly the speed of light, then it speed of light, then it will have a stretched will have a stretched out wavelength and out wavelength and lower frequency (less lower frequency (less energy).energy).

This is also known as This is also known as Red Shift.Red Shift.

LightLight Light is known as an Light is known as an

Electromagnetic wave.Electromagnetic wave. But, light is also But, light is also

known as a photon.known as a photon. Light is both a particle Light is both a particle

and a wave.and a wave. This is called the This is called the

Duality of Light.Duality of Light. Light is a particle with Light is a particle with

a wave-like a wave-like characteristic.characteristic.

More lightMore light Light does not Light does not

need a medium to need a medium to travel, neither do travel, neither do any of the EM any of the EM waves.waves.

Light travels at it’s Light travels at it’s own speed.own speed.

The speed of light The speed of light is 3.00 x 10is 3.00 x 1088 m/s or m/s or 186,000 miles/sec.186,000 miles/sec.

Light travels in Light travels in straight lines.straight lines.

The photon is a The photon is a packet of energy.packet of energy.

Einstein showed that Einstein showed that light was a particle.light was a particle.

He was able to show He was able to show that the momentum that the momentum of the photon was of the photon was able to move able to move electrons, causing electrons, causing electricity to be electricity to be produced.produced.

Waves BounceWaves Bounce When a sound wave When a sound wave

bounces, we call it an bounces, we call it an echo.echo.

When a light wave When a light wave bounces, we call it a bounces, we call it a reflectionreflection

The law of reflection The law of reflection says that the says that the reflected ray bounces reflected ray bounces off at the same angle, off at the same angle, to the normal, as the to the normal, as the incoming ray.incoming ray.

Flat MirrorFlat Mirror A flat mirror (flat surface) will reflect a true A flat mirror (flat surface) will reflect a true

image.image. This image will appear as if it were a copy of the This image will appear as if it were a copy of the

original.original.

Concave MirrorConcave Mirror

Concave mirrors follow the law of reflections.Concave mirrors follow the law of reflections. Concave mirrors have the reflective surface Concave mirrors have the reflective surface

on the inside of the curve.on the inside of the curve.

If an object is beyond the focal point of If an object is beyond the focal point of the concave mirror, then the image is the concave mirror, then the image is smaller and inverted.smaller and inverted.

If an object is within the focal point of the If an object is within the focal point of the concave mirror, then the image is concave mirror, then the image is magnified.magnified.

Convex Mirror Convex Mirror

A convex mirror has A convex mirror has its reflective surface its reflective surface on the outside of the on the outside of the curve of the mirror.curve of the mirror.

Therefore, the focal Therefore, the focal point is inside the point is inside the mirror, and the object mirror, and the object of the reflection can of the reflection can not reach that focal not reach that focal point.point.

Images seen in a Images seen in a convex mirror convex mirror appear as smaller, appear as smaller, right-side up, and right-side up, and the view is spread the view is spread out more.out more.

RefractionRefraction

Refraction is when a Refraction is when a light wave travels light wave travels through a medium through a medium and bends. and bends.

Whenever, light Whenever, light enters or exits a enters or exits a medium, the light medium, the light rays bend.rays bend.

A medium is a A medium is a material that waves material that waves travel through.travel through.

As the incoming light As the incoming light enters the medium at enters the medium at an angle, the an angle, the medium bends that medium bends that light according to its light according to its “index of refraction”.“index of refraction”.

This index is constant This index is constant for each medium.for each medium.

The different The different mediums also cause mediums also cause the light to change the light to change speeds.speeds.

This bending of the light This bending of the light gives us the illusion that gives us the illusion that the objects are bent or in the objects are bent or in different locations when different locations when they are in water.they are in water.

LensesLenses Like mirrors, there are 2 different types of Like mirrors, there are 2 different types of

lenses.lenses. A concave lens is curved so the open part is A concave lens is curved so the open part is

the inside of the curve.the inside of the curve.

All lenses follow the same law of All lenses follow the same law of refraction.refraction.

Light bends as it goes through a lens.Light bends as it goes through a lens.

Convex LensConvex Lens

Convex lenses have the medium within Convex lenses have the medium within the curve of the lens.the curve of the lens.

Unlike the concave lens, which bends the Unlike the concave lens, which bends the rays outward, convex lenses bend the rays rays outward, convex lenses bend the rays inward to a single point.inward to a single point.

The Electro-Magnetic The Electro-Magnetic SpectrumSpectrum The electro-magnetic spectrum is also The electro-magnetic spectrum is also

referred to as the EM spectrum.referred to as the EM spectrum. This spectrum consists of waves that are This spectrum consists of waves that are

driven by electric fields and magnetic driven by electric fields and magnetic fields that continuously create each other.fields that continuously create each other.

Unlike other waves, the EM waves do not Unlike other waves, the EM waves do not need a medium to propagate.need a medium to propagate.

All EM waves (including light) travel at 3.0 All EM waves (including light) travel at 3.0 x 10x 1088 m/s or 186,000 miles/second. m/s or 186,000 miles/second.