1 WAVES

1) Recognize that all waves transfer energy. 2) Explain the Doppler Effect in terms of everyday interactions. 5) Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves. 3) Relate frequency & wavelength to the energy of different types of electromagnetic waves & mechanical waves. 6) Explain the phenomena of reflection, refraction, interference, & diffraction. 4) Relate the speed of sound to different mediums. 2

3 Waves Waves are disturbances that carry energy through matter or space. Clip Waves can be visible or invisible evidence of energy transfer. The material does not actually travel with the wave….. only the energy is carried.

Types of Waves Two types of waves: 4 Two types of waves: Mechanical Non-Mechanical Mechanical: waves need a medium in order to travel. Examples: Sound, water Non-mechanical: waves do not need a medium to travel. Examples: light, gamma waves, microwaves, x-rays

5 Mechanical Waves Waves that require a medium to travel. A medium is the material a wave travels through (solid, liquid, gas, vacuum) Sound and water. Light waves are NOT Mechanical Waves.

Ways that waves travel Transverse waves (left box) 6 Ways that waves travel Transverse waves (left box) Water, light Compressional waves (right box) AKA: Longitudinal Waves sound

Transverse Waves Transverse waves are UP & DOWN movements. 7 Transverse Waves Transverse waves are UP & DOWN movements. The displacement of individual particles is perpendicular (at right angles) to the direction of the wave. EX: water waves, radio waves (all EM waves)

Describing a Transverse Wave 8 Describing a Transverse Wave

Movement of a Transverse Wave 11 9 Movement of a Transverse Wave CLIP

Remember: Energy is transferred ----NOT THE MATTER!-- 12 Example - Water Remember: Energy is transferred ----NOT THE MATTER!--

Compressional Waves 13 Compressional waves are a series of PUSHES & PULLS in which the motion of the medium is in the same direction as the wave Ex. Sound Waves

Parts of a Compressional Wave 15 Compressions & Rarefactions Rarefaction is a place where the atmospheric pressure is lowest- molecules are spread out (behind the compression).

Characteristics of a Compressional Wave 14

Energy moves this way

Wavelength of Transverse and Compressional Waves Comparison

Amplitude of Compressional Wave Tighter compressions=Higher amplitude=Higher Energy

Transverse Waves

Compressional Waves

Concept Check Light (EM waves)…. is a mechanical wave or a non-mechanical wave travels as a transverse wave or a compressional wave Sound.…. is a mechanical wave or a non-mechanical wave travels as a transverse wave or acompressional wave

The higher the amplitude, the more energy the wave is carrying 9 amplitude The higher the amplitude, the more energy the wave is carrying In a compressional wave- it’s how tightly the compressions are.

Frequency Number of waves per second. 10 Number of waves per second. How many waves pass a certain point every sec. Unit: Hertz 1 wave per second= 1 Hz

λ Wavelength Wavelength 10 λ Wavelength Distance between two identical points on adjacent waves. Measured in Meters As the wavelength decreases,… the frequency increases

Speed of a wave ν = f λ ν is the velocity (m/s) 16.1 Speed of a wave ν = f λ ν is the velocity (m/s) f is the frequency (hertz) λ is the wavelength (m) The speed of a mechanical waves is constant for any given medium.. The speed of a wave changes as it moves through different media

Let’s do some practice problems. 16.2 ν = f xλ Let’s do some practice problems.

Wave interactions with matter

Wave interactions with matter 17 Wave interactions with matter Reflection occurs when a wave hits another wave or object that it cannot pass through and bounces back.

Law of Reflection

Refraction occurs when a wave passes from one medium to another at an angle and bends (changes direction) due to a change in speed. 18

Refraction

19 Diffraction occurs when a wave passes through an opening and spreads out Diffraction is a wave phenomenon that is dependent on wavelength Light waves bend as they pass by the edge of a narrow aperture or slit 

Diffraction

When a wave encounters an obstacle. Apparent bending of waves around small obstacles and the spreading out of waves past small openings.

20 Constructive Interference occurs when two or more waves hit the same point and combine to produce a larger single wave.

20 Destructive Interference occurs when two or more waves hit the same point and combine to produce a smaller single wave.

Constructive Interference Clip Constructive Interference Destructive Interference

Two waves interfering with each other… constructively and destructively.

Concept Check B A 1)Which waves has a higher amplitude? 2) Which light wave will go faster? a) light traveling in a vacuum b) light traveling in glass 3) What is causing the rainbow of colors to appear from the prism?

Review of Waves Properties of Mechanical Waves-video clip

Review of Waves

Review of Waves

GOALS REVISITED. Recognize that all waves transfer energy. Explain the phenomena of reflection, refraction, interference, & diffraction. Relate frequency & wavelength to the energy of different types of electromagnetic waves & mechanical waves. GOALS REVISITED. Relate the speed of sound to different mediums. Explain the Doppler Effect in terms of everyday interactions. Compare and contrast the characteristics of electromagnetic and mechanical (sound) waves. 2