Waves Chapter 17

Key Terms w Wave- a disturbance that transmits energy through matter or space w Medium- the matter through which a wave travels w Mechanical wave- a wave that requires a medium through which to travel w Electromagnetic wave- caused by a disturbance in electric and magnetic fields. Does not require a medium

Waves transfer energy w Ability to do work w waves carry energy w bigger the wave, the more energy it carries w Energy may spread out as the wave travels w Wave spread out in spheres that get bigger as the wave moves from the center

Transverse and longitudinal waves w Transverse waves include all electromagnetic [radio, radar, i.r., visible, u.v., X-rays] w have perpendicular motion  w longitudinal waves are sound waves. w Have parallel motion 

Wave properties w A wave is a pattern in the value of some quantity which is changing at every point of space.

Wave Properties w Crest- Highest point of a transverse wave w Trough- the lowest point of a transverse wave w Amplitude- greatest distance that particles in a medium move from their normal position when a wave passes w The amplitude is the height of the wave. w The wavelength is the distance from one wave top, or crest, to the next.

amplitude wavelength

Wave properties w Frequency refers to how many waves are made per time interval. This is usually described as how many waves are made per second, or as cycles per second. w Period- Time required for one full wavelength to pass a certain point. w w

Frequency- Period Equation

Wave speed w The speed at which a wave passes through a medium w Wave speed, wavelength, and frequency are related by the equation: v = f λ w The speed of a wave depends upon the material it is traveling through.

Doppler effect w Whenever relative motion exists between a source of sound and a listener, the frequency of the sound is as heard by the listener is different compared to the frequency when there is no relative motion

The Doppler Effect w Heard an ambulance go by recently? Remember how the siren's pitch changed as the vehicle raced towards, then away from you? First the pitch became higher, then lower. Originally discovered by the Austrian mathematician and physicist, Christian Doppler ( ), this change in pitch results from a shift in the frequency of the sound waves w As the ambulance approaches, the sound waves from its siren are compressed towards the observer. The intervals between waves diminish, which translates into an increase in frequency or pitch (f f f f f ) w As the ambulance recedes, the sound waves are stretched relative to the observer, causing the siren's pitch to decrease. By the change in pitch of the siren, you can determine if the ambulance is coming nearer or speeding away. If you could measure the rate of change of pitch, you could also estimate the ambulance's speed.

Doppler Effect w By analogy, the electromagnetic radiation emitted by a moving object also exhibits the Doppler effect. w The radiation emitted by an object moving toward an observer is squeezed; its frequency appears to increase and is therefore said to be blue-shifted. w In contrast, the radiation emitted by an object moving away is stretched or red-shifted. w As in the ambulance analogy, blue-shifts and red-shifts exhibited by stars, galaxies and gas clouds also indicate their motions with respect to the observer.  f

Standing Waves w Standing waves are non-traveling vibrations of certain wavelength and frequency which occur on a medium of certain size w The size of the medium controls the wavelengths of the standing waves w the way that the medium is held at its ends, either fixed or open, controls the wavelengths of the standing waves. w

Node and antinodes w Node- medium does not move and have no vibration w Antinode- form where the crests of the original waves line up with crests of the reflected waves so that complete constructive interference occurs w Point of maximum vibration