Waves and Wave Waves and Wave InteractionsInteractions

Chapter 14 - 15Chapter 14 - 15

Physical SciencePhysical Science

Waves

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

• Medium – the environment that the wave Medium – the environment that the wave travels in (ex: water, air)travels in (ex: water, air)

Waves Transfer Waves Transfer EnergyEnergy

• Waves will spread out in all directions Waves will spread out in all directions carrying energy. carrying energy.

• The energy is conserved in the system The energy is conserved in the system following both the law of conservation of following both the law of conservation of momentum and energy.momentum and energy.

Waves transfer EnergyWaves transfer Energy

• EX: Water waves do work on a boatEX: Water waves do work on a boat

• EX: Sound waves do work on your EX: Sound waves do work on your eardrumeardrum

• EX: Light waves do work on your eyeEX: Light waves do work on your eye

Energy of WavesEnergy of Waves

Wave Speed• The speed of a wave will depend on The speed of a wave will depend on

the medium it travels throughthe medium it travels through• The state of matter determines the The state of matter determines the

speed of the wave.speed of the wave.– EX: In gases the particles are spread out EX: In gases the particles are spread out

so the wave travels slower in gasesso the wave travels slower in gases– EX: In liquids, the particles are closer EX: In liquids, the particles are closer

together so the energy is transferred together so the energy is transferred quicker between particles of that mediumquicker between particles of that medium

– EX: In solids, the particles are tightly EX: In solids, the particles are tightly packed together so the wave travels very packed together so the wave travels very quickly through solidsquickly through solids

Parts of a WaveParts of a Wave

Doppler Effect – Doppler Effect – Occurs when the wave source is movingOccurs when the wave source is moving..

http://www.physicslessons.com/phe/dopplereff.htm

• Image Simulation

•Breaking the sound barrier

Light WavesLight Waves

• Light waves occur in different frequencies Light waves occur in different frequencies and wavelengthsand wavelengths

• Light waves are represented on the Light waves are represented on the electromagnetic spectrumelectromagnetic spectrum

• The Electromagnetic Spectrum consists The Electromagnetic Spectrum consists of visible light and other waves that of visible light and other waves that cannot be seen.cannot be seen.

Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic SpectrumElectromagnetic Spectrum

The Electromagnetic The Electromagnetic SpectrumSpectrum

• Consists of light at all possible Consists of light at all possible energies, frequencies, and energies, frequencies, and wavelengths.wavelengths.

• Visible light is only a small part of the Visible light is only a small part of the spectrum.spectrum.

• The spectrum also contains X-rays, The spectrum also contains X-rays, Ultraviolet rays, Radio Waves, Ultraviolet rays, Radio Waves, Gamma waves. Gamma waves.

The Nature of LightThe Nature of Light• Light acts as a wave in that it:Light acts as a wave in that it:

– produces interference patterns like water wavesproduces interference patterns like water waves– Follows the laws of reflection, diffraction, and Follows the laws of reflection, diffraction, and

refractionrefraction

The Nature of LightThe Nature of Light

• Light also acts as a particleLight also acts as a particle– These particles are called PHOTONSThese particles are called PHOTONS– A beam of light is considered to be a A beam of light is considered to be a

stream of photons.stream of photons.– Photons do not have mass…they are like Photons do not have mass…they are like

“bundles of energy”“bundles of energy”

Light Wave SpeedLight Wave Speed

• All electromagnetic waves in empty All electromagnetic waves in empty space travel at the same speedspace travel at the same speed

• The speed of light is: 3.00 x 10The speed of light is: 3.00 x 1088 m/s or m/s or 186,000 miles/second186,000 miles/second

• Light will travel slower when it has to Light will travel slower when it has to pass through a medium such as air or pass through a medium such as air or waterwater

Wave InterferenceWave Interference

Wave InterferenceWave Interference

• The combination of two or more The combination of two or more waves of the same frequency that waves of the same frequency that result in a single waveresult in a single wave

• Two types:Two types:– Constructive InterferenceConstructive Interference– Destructive InterferenceDestructive Interference

Constructive InterferenceConstructive Interference

• Occurs when two waves meet and produce Occurs when two waves meet and produce a larger wave.a larger wave.

Destructive InterferenceDestructive Interference• Occurs when two waves meet and make a Occurs when two waves meet and make a

smaller wave or cancel each other out.smaller wave or cancel each other out.

Wave InterferenceWave Interference

• Interference of Light Waves produce Interference of Light Waves produce colorful displayscolorful displays

• Ex: Soap bubbles often show reds, Ex: Soap bubbles often show reds, blues, and yellows on their surface blues, and yellows on their surface because of the interference of light.because of the interference of light.

Wave Interference Wave Interference SimulationSimulation

Wave InteractionsWave Interactions

Wave InteractionsWave Interactions

• Waves may interact with each other Waves may interact with each other when traveling through a mediumwhen traveling through a medium

• There are 3 possible outcomes:There are 3 possible outcomes:– Reflection, Diffraction, and RefractionReflection, Diffraction, and Refraction

1. Diffraction1. Diffraction

• A change in the direction of a wave when A change in the direction of a wave when the wave finds an obstacle or an edgethe wave finds an obstacle or an edge

2. Reflection2. Reflection

• The bouncing back of a wave when the wave The bouncing back of a wave when the wave hits a surface or boundaryhits a surface or boundary

Reflection of lightReflection of light

• Every object reflects some lightEvery object reflects some light

• Rough surfaces reflect light in many Rough surfaces reflect light in many directionsdirections

• Smooth surfaces reflect light in one Smooth surfaces reflect light in one directiondirection

Law of ReflectionLaw of Reflection

• When light hits a When light hits a smooth surface, smooth surface, the angle of the angle of incidence equals incidence equals the angle of the angle of reflection.reflection.

3. Refraction3. Refraction• The bending of The bending of

waves when they waves when they pass from one pass from one medium to anothermedium to another

• Causes the wave to Causes the wave to bendbend

• Prism Example:Prism Example:

• http://http://www.physicslessons.www.physicslessons.com/exp33.htmcom/exp33.htm

Laws of RefractionLaws of Refraction• When light travels in a medium with a When light travels in a medium with a

higher speed to a medium where it slows higher speed to a medium where it slows down, the ray is bent toward the normaldown, the ray is bent toward the normal

Laws of RefractionLaws of Refraction• When light travels from a medium where it When light travels from a medium where it

is slower to a medium where it can travel is slower to a medium where it can travel faster, light bends away from the normalfaster, light bends away from the normal

RefractionRefraction

• Because of Because of refraction images refraction images appear to be in appear to be in different positionsdifferent positions

Wave AbsorptionWave Absorption

• Energy from the Energy from the wave is wave is absorbed into absorbed into the medium the medium

• Often as heat Often as heat (measured as (measured as thermal energy).thermal energy).

Thermal EnergyThermal Energy

• Thermal conductors have a high rate of Thermal conductors have a high rate of energy transferenergy transfer

• Thermal insulators have a slow rate of Thermal insulators have a slow rate of thermal energy transferthermal energy transfer

• Rate of thermal energy transfer is Rate of thermal energy transfer is dependent on temperature, color, texture dependent on temperature, color, texture and exposed surface area of the object.and exposed surface area of the object.

Thermal EquilibriumThermal Equilibrium

• The amount of thermal energy The amount of thermal energy absorbed is equal to the amount of absorbed is equal to the amount of thermal energy emitted. thermal energy emitted.

• The temperature remains constant.The temperature remains constant.