Objectives

• Recognize that waves transfer energy.

• Distinguish between mechanical waves and electromagnetic waves.

• Explain the relationship between particle vibration and wave motion.

• Distinguish between transverse waves and longitudinal waves.

Chapter 14

Bellringer1. Imagine throwing a rock into a pond or lake.

Describe the effect that the rock has on the surface of the water.

2. When surfing, a person moves just ahead of a wave. Where does the energy come from to move the surfer through the water?

3. What happens to a string on a guitar or other stringed instrument when it is plucked?

4. When a musician strikes two cymbals together, the cymbals will begin to vibrate and make music. How does the musician stop the music?

Chapter 14

Energy and Waves

Waves: water, sound , and light all travel in wavesWavelength: () the distance between peaks of a

wave. (usually in meters)Frequency: the number of waves that pass a

given point in a specific time, usually one second. (Hertz)

Hz or 1/s LONG

SHORT

• Transverse waves: waves where particles move up and down– When the wave moves through the medium, the

particles are bumped perpendicular to the wave….in other words….away from the wave.

• Longitudinal Waves: the particles vibrate back and forth (they are not bumped up and down). – Pushing a spring back and forth creates a

longitudinal wave

So what is the difference?......• A) is a Longitudinal wave – back and forth-

vibrations – aka… oscillations. • B) is a transverse wave – up and down

• http://physics-animations.com/Physics/English/top10.htm

What do waves do?1) Waves carry energy away from its source. 2) Waves carry energy, but not matter3) As a wave travels, it uses energy to do work on

everything in its path4) Waves are energy traveling through matter and

acting on that matter (making it move or heat up)5) The matter that it travels through can move two

different ways depending on the type of wave. – The object can move up and down- like a leaf floating

and moving as the waves of a pond move toward the shore

– The object can move in circles- like ocean waves where water meets air

Water Wave Motion

Section 1 Types of WavesChapter 14

Objectives

• Identify the crest, trough, amplitude, and wavelength of a wave.

• Define the terms frequency and period.

• Solve problems involving wave speed, frequency, and wavelength.

• Describe the Doppler effect.

Chapter 14

Bellringer

There are many different types of waves. You may be familiar with the electromagnetic spectrum, which includes radio waves, microwaves, infrared light, visible light, ultraviolet light, X rays, and gamma rays.

1. Name five common applications of waves in the electromagnetic spectrum, and list the type of wave used in each case.

2. Lasers are made from accurately focused visible light waves that are produced in phase with each other. Lasers made from visible light waves are often used in surgery to perform delicate procedures and to seal the area being treated.

Chapter 14

Part of a wave• Crest: High point of a transverse wave• Trough: lowest point of a transverse wave

• Compression: crowded area of longitudinal waves

• Rarefaction: the expanded part of the longitudinal wave

• Amplitude: the height of the peak – measured from the rest position– It takes more energy to move far from rest position

• Wavelength : distance between …..– Two adjacent Peaks of transverse waves – Two adjacent compressions of longitudinal wave

Rest position

Amplitude

Greater AmplitudeHigher EnergyLouder Sound

Smaller AmplitudeLower EnergySofter Sound

Waves• Wave: a wave is produced by a vibrating object.– Mechanical Waves: a wave that passes through

matter, and causes the matter to vibrate, but the energy of the wave passes through. (resonance)• Requires a medium (substance like solid, liquid, gas)• Like sound waves or ocean waves• If there are no particles to vibrate, then nothing happens,

no motion, no sound…..nothing!– Electromagnetic wave: waves that transfer energy

without travelling through a matter)• Does not require a medium• Like x-rays, and ultraviolet, infrared, and radio waves

Speed of a wave (C): – The speed of a wave depends on the medium it is traveling

through– Speed of light: 3 x 108 m/s (traveling through air)– Speed of sound: 340 m/s (traveling through air)

C = • Wavelength and Frequency are opposites. • (they are indirectly related) • One goes up to other goes down.

E = h• Energy and Frequency are the same.• (they are directly related)• One goes up the other also goes up.

FrequencyChapter 14

How Light Works• Photon: a particle of electromagnetic radiation that

has energy and no mass. (tiny packets of energy)• Different wavelengths of light carry different

amounts of energy• The energy in a photon depends on the amount of

energy released when an atom goes from an excited state to a ground state

• Ground State: the lowest energy state of an atom• Excited State: the high energy state of an atom– when excited atoms return to their ground state, they

emit energy/photon of radiation. ( example: Neon signs)

• Line-emission spectrum: bands of light resulting from a narrow beam of light shined through a prism.

• The emission spectrum of each element is unique

Emission Spectrum

Line and absorption spectra

Electromagnetic Radiation:

• energy that exhibits wave like behavior as it travels through space.

• moves at the speed of light• Electromagnetic radiation is usually called light. It is

divided into various classes• Gamma rays, X-rays, ultraviolet and infrared light,

microwaves, and radio waves form the electromagnetic spectrum

The Electromagnetic SpectrumChapter 14

• Gamma-rays: radioactive materials• X-rays: pass through soft body tissue but are

stopped by harder tissue, like bone• Ultraviolet: part of sunlight that causes sunburn

and cancer. – The ozone absorbs most of the sun’s UV rays– Stars and other "hot" objects in space emit UV

radiation• Visible light: part of the spectrum to which our eyes

are sensitive– our eyes and brain interpret different frequencies as

different colors– ROYGBIV

• Infrared: radiation given off by the human body and most other warm objects. (fire, heaters)

• Microwaves: used for communications and cooking• Radio: lowest frequencies of the spectrum

Bellringer

1. The back of a mirror is flat and highly reflective. Describe how you think a mirror works.

2. Why do you think one piece of safety equipment that backpackers carry into the wilderness is a mirror?

3. Describe what an echo is.

4. Blinds in the windows of homes, schools, and offices can be tilted up or down, or they can be closed completely. Explain how varying positions of the blinds controls light.

Chapter 14

What can we do to waves?• Reflect them: when a wave bounces back after

hitting something • Refract them: when a wave is bent or broken down

because it starts travelling in a new medium – light through a prism– Because the speed of a wave depends on the medium it

is in, when the wave enters a new medium, it starts to travel at a different speed, thus is bends)

• Diffract them: waves that travel around a barrier or through an opening – Like sound that travels around a corner so that you can

hear it.

Reflection, Diffraction, and Refraction

• Reflection is the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through.Waves reflect at a free boundary.The reflected wave is exactly like the original wave

except that the reflected wave is traveling in the opposite direction to the direction of the original wave.

At a fixed boundary, waves reflect and turn upside down.

Chapter 14

Reflection

Refraction in lenses and reflection in mirrors

Reflection

Chapter 14

Reflection, Diffraction, and Refraction

• Mirrors– Flat form virtual images…brain interprets light so

images appear as far behind the mirror as the object s in front of it

– Curved distort images• Concave form real images…light rays actually focused• Convex…side view mirror, traffic mirrors

Reflection, Diffraction, and Refraction

• Refraction: light waves bend or refract when they pass from one medium to another– Makes objects appear to be in different positions– Creates mirages– Fiber optics– Lenses…microscopes, telescopes, glasses, eyes!– Prisms– Rainbows (reflection and refraction)

Lawnmower analogy for refraction

Refraction

Refraction and reflection

Refraction in lenses and reflection in mirrors

Diffraction

• Diffraction…wave encounters an obstacle or a slit. Involves interference.

Constructive and Destructive Interference

• Constructive interference increases amplitude.• Constructive interference is any interference in

which waves combine so that the resulting wave is bigger than the original waves.• The amplitude of the resulting wave is the sum of the amplitudes of

the two individual waves.

• Destructive interference decreases amplitude.• 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, continued• Interference of light waves creates colorful displays.

• Interference of sound waves produces beats.When two waves of slightly different frequencies interfere

with each other, they produce beats.

Chapter 14

Standing Waves• Interference can cause standing waves.

• A standing wave is a pattern of vibration that simulates a wave that is standing still.

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

• Although it appears as if the wave is standing still, in reality waves are traveling in both directions.

• Standing waves have nodes and antinodes.• Each loop of a standing wave is separated from the

next loop by points that have no vibration, called nodes.• Nodes lie at the 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, causing complete constructive interference.

• Standing waves can have only certain wavelengths.• In general, standing waves can exist whenever

a multiple of half-wavelengths will fit exactly in the length of the string.

• It is possible for standing waves of more than one wavelength to exist on a string at the same time.

Chapter 14

Doppler Effect• Pitch is determined by the frequency of sound waves.

• The pitch of a sound, how high or low it is, is determined by the frequency at which sound waves strike the eardrum in your ear.

• A higher-pitched sound is caused by sound waves of higher frequency.

• Frequency changes when the source of waves is moving.• The Doppler effect is an observed change in the frequency

of a wave when the source or observer is moving.