Waves

What is a Wave?

"A wave can be described as a disturbance that travels through a medium from one location to another location ."

Transverse Wave Motion

A group of people jumps up and sits back down, some nearby people see them and they jump up, some people further away follow suit and pretty soon you have a wave travelling around the stadium. The wave is the disturbance (people jumping up and sitting back down), and it travels around the stadium. However, none of the individual people the stadium are carried around with the wave as it travels - they all remain at their seats

Transverse wave

In a transverse wave the particle displacement is perpendicular to the direction of wave propagation

The particles do not move along with the wave; they simply oscillate up and down about their individual equilibrium positions as the wave passes by .

Light waves are transverse in nature.

Transverse waves on a string The string is displaced up and down as the

wave travels from left to right, but the string itself does not experience any net motion.

Transverse wave

TRANSVERSE WAVE

VIBRATIONS ARE AT 90O OR

RIGHT ANGLES TO WAVE DIRECTION

WAVE DIRECTION

vibrations

longitudinal wave

In a longitudinal wave the particle displacement is parallel to the direction of wave propagation The particles do not move down the tube with the wave; they simply oscillate back and forth about their individual equilibrium positions. Pick a single particle and watch its motion

Sound waves are longitudinal

LONGITUDINAL WAVE

WAVE DIRECTION

VIBRATIONS ARE PARALLEL

TO WAVE DIRECTION

vibrations

Parts of a waveThe crest of a wave is the point on the medium

which exhibits the maximum amount of positive or upwards displacement from the rest position

The trough of a wave is the point on the medium which exhibits the maximum amount of negative or downwards displacement from the rest position.

AmplitudeThe amplitude of a wave refers to the

maximum amount of displacement of a particle on the medium from its rest position.

Wavelength The wavelength of a wave is the distance between

any two adjacent corresponding locations on the wave train.

This distance is usually measured in one of three ways: crest to next crest, trough to next trough, or from the start of a wave cycle to the next starting

point.

Diagram of a wave

WAVELENGTH

WAVELENGTH

PEAK OR CREST

TROUGH

AM

PL

ITU

DE

All waves are caused by vibrations

Frequency and Time periodThe frequency (f) of a wave is the

number of cycles that pass the observer in a given time.

Hertz is the unit of frequency. Frequency and period are exact

inverses of each other,        f = 1 / T or T = 1 / f

Finding the relationship between

WAVESPEED, FREQUENCY & WAVELENGTH

Frequency =

10m

0s 0.5s

4Hz

Wavelength = 5 m

Wavespeed = 20 m/s

What is the relationship?

wave speed (m/s) = frequency (Hz) x wavelength (m)

x

WS

F WL

WS = F x WL

F = WS

WL

WL = WS

F

Wave Equation

The relation between the speed (v) of a wave ,its wavelength (λ) and frequency (f) is given by

Speed = Wavelength x Frequency

Using the symbols v, λ , and f, the equation can be rewritten as

v = f x λ

1. If the speed of a wave is 340m/s, and its wavelength is 20m, what is its frequency?

wave speed = frequency x wavelength

340 = frequency x 20

frequency = 340 = 17 Hz

20

2.If 300 cycles are produced in 60s and the wavelength is 10m, find:-

(a) the frequency

300 cycles

60s

(b) the wave speed

wave speed = frequency x wavelength

= 5 cycles/s = 5 Hz

= 5 x 10 = 50 m/s

3.Light waves travel at 300 000 000 m/s. If their frequency is 500Hz, find their wavelength

wave speed = frequency x wavelength

300 000 000 = 500 x wavelength

300 000 000 =

500

600 000 m

4. If 25 cycles occur in 1 second and their wavelength is 3 metres, find the wave speed

wave speed = frequency x wavelength

= 25 x 3

= 75 m/s

PEAK/CREST

WAVELENGTH

WAVEFRONTS

WAVEFRONTS (PEAK/CREST OF WAVES FROM ABOVE)

Circular Wavefronts

Each line is a peak/crest of a circular wave

Diffraction of Waves

Diffraction means spreading out. This can occur to waves

when they go through a small gap.

Diffraction (spreading out) of waves through a gap equal or smaller than the wavelength

Peaks or Crests of Waves

Spreading out

Diffraction (spreading out) of waves through a gap larger than the wavelength

Peaks or Crests of WavesSmall amount of spreading out

Wave A

Wave B

Output

CONSTRUCTIVE

INTERFERENCE

Wave A

Wave B

Output

DESTRUCTIVE

INTERFERENCE

Wave A

Wave B

Resultant

Wave

Interference of Waves

Peak meets Peak

or

Trough meets Trough

Constructive Interference

Interference of overlapping

waves

Peak meets Trough

Destructive Interference

Interference of overlapping

waves

Hope you enjoyed Learning