W AVES

W AVES AND E NERGY  Waves and Energy  Wave – a traveling disturbance that carries energy from one place to another  Waves do not carry matter; waves carry energy  Vibration – movement that follows the same path over and over again  Wave – movement of energy from a vibrating source outward

Medium  The matter or substance through which a wave is transmitted Ex. Water – medium for ocean waves Air – medium for sound

M ECHANICAL WAVES  waves that require a medium  Ex. Sound and water waves

E LECTROMAGNETIC WAVE  Wave that consists of electric and magnetic fields  Do not require a medium  Ex. Light, microwaves, x-rays

C HARACTERISTICS OF W AVES  Amplitude  Wavelength  Frequency

Amplitude  Greatest distance from normal resting position to top (crest) of the wave  Indicates the amount of energy carried by the wave

Wavelength  Distance between two crests or two troughs (lowest point)  Usually measured in meters or centimeters  Symbol for wavelength is lambda λ

Frequency  Frequency – the number of complete waves or complete cycles per unit time  Unit: Hertz (Hz) = 1 wave/second

T YPES OF WAVES  Transverse waves  Longitudinal Waves  AKA compressional wave

T RANSVERSE WAVES  A wave in which the motion of the medium is at right angles to the direction of the wave Movement of particles is up and down – vertical Movement of the wave is horizontal  Ex Waves on a rope, water waves, light, electromagnetic waves

L ONGITUDINAL W AVES  AKA compressional wave  Wave in which the motion of the medium is parallel to the direction of the wave  A series of compressions and rarefactions  Rarefaction – space in the medium in which there are fewer particles  Ex Sound waves

S PEED OF W AVES  Speed = frequency x wavelength  Speed of a wave is constant within the same given medium  If frequency is increased then wavelength must decrease for constant speed to be maintained

The speed of a wave depends upon the medium  The density of the medium affects the speed of mechanical waves o The more dense a medium, the slower light waves travel but the faster sound waves travel.

Elasticity of the medium affects the speed of waves  Elasticity – ability of a medium to return quickly to its original shape after being disturbed  The more elastic – the faster the wave

W AVE I NTERACTIONS  Reflection  Refraction  Diffraction  Interference  Standing waves  Resonance

R EFLECTION  Bouncing back of waves upon reaching another surface  Echo  Mirror image

L AW OF R EFLECTION  The angle of incidence (i) is equal to the angle of reflection (r)  Ray – line drawn in the direction of motion of a wave Incidental ray – incoming ray (incoming wave) Reflected ray – ray (wave) that bounces off barrier  Angle of incidence (i) – angle formed by the incident ray and the normal  Angle of reflection (r)- angle formed by the reflected ray and the normal  Normal – line drawn perpendicular to barrier

Refraction  The speed of a wave changes as the wave travels from one medium to another  Refraction – the bending of waves due to a change in speed  Refraction occurs because waves move at different speeds in different mediums  If wave slows down it is bent to the normal  If it speeds up, it is bent away from the normal

D IFFRACTION  The bending of waves around the edge of an obstacle or through a narrow opening

I NTERFERENCE  Interaction of waves that occur at the same place at the same time; the wave combine to make a single wave  Constructive interference – crest meets crest; the amplitudes add together creating a larger amplitude  Destructive interference – crest meets trough; the amplitudes subtract from one another creating a smaller amplitude

E XAMPLE OF DESTRUCTIVE I NTERFERENCE

S TANDING W AVES  Wave that does not appear to be moving; occurs at the natural frequency of the material  Nodes – points at which destructive interference results in no energy displacement  Antinodes – points at which constructive interference causes maximum energy displacement  Resonance frequency – frequency at which a standing wave occurs

R ESONANCE  The ability of an object to vibrate by absorbing energy at its natural frequency  Video Video  Video 2 Video 2

P OLARIZATION  Alignment of vibrations in a transverse wave  Usually by filtering out waves of other directions  Polarizing filters – transmit only light waves that vibrate in the same plane  Polarized sun glasses Reduce glare