Waves

Page 1

Progressive waves

DEFINITIONS

reflection-the wave is bounced back when it hits a boundary

refraction- the wave changes direction as it enters a different medium

diffraction- the wave spreads out as it passes through a gap or round an obstacle

displacement- how far a point on the wave has moved from its undisturbed position

amplitude- the maximum magnitude of the displacement , the distance from the undisturbed position to the crest or trough

wavelength- the length of one whole wave oscillation or wave cycle

period- the time for one whole wave cycle

frequency- the number of whole wave cycles per second passing a given point

phase- a measurement of the position of a certain point along the wave cycle

phase difference- the amount by which one wave lags behind another wave

a progressive wave carries energy from one place to another without transferring any material

a wave is caused by something making particles or fields oscillate

measuring waves

displacement (x) measured in metres

amplitude (A) measured in metres

wavelength (λ) measured in metres

period (T) measured in seconds

frequency (f) measured in hertz

Page 2

Wave Speed

EQUATIONS

speed=distance ÷ time

from this we can get the equation

c=fλ

c= wave speed in ms-1

f=frequency in Hz s-1

λ= wavelength in m

c= λ/(1/f) = fλ

electromagnetic wave speed in a vacuum

speed of light (c) = 3x10^8 ms-1

measuring the speed of sound

two microphones in a straight line a distance of d apart

separate inputs so the signals from each can be recorded separately

signal generator used to produce sound from the loudspeaker

use computer to to record time between the two microphones to pick up the sound

measuring the time delay between the first peak of the signal received by each microphone on a graph of voltage against time

use speed = distance/time to calculate speed