Diagram of a wave

WAVELENGTH

WAVELENGTH

PEAK OR CREST

TROUGH

AM

PL

ITU

DE

All waves are caused by vibrations

0s 1s

0s1s

Frequency is the number of complete cycles or vibrations occurring every second. It is measured in HERTZ (Hz)

2 cycles in 1s = 2Hz

4 cycles in 1s = 4Hz

LONGITUDINAL WAVE

WAVE DIRECTION

VIBRATIONS ARE PARALLEL

TO WAVE DIRECTION

vibrations

TRANSVERSE WAVE

VIBRATIONS ARE AT 90O OR

RIGHT ANGLES TO WAVE DIRECTION

WAVE DIRECTION

vibrations

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

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 Waves

Small 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

Plane boundary e.g. mirror

Reflection of light at a plane boundary e.g. mirror

Incident Angle

I

Reflective Angle

r

Incident Angle (i) = Reflected Angle (r)

Plane Boundary

Reflection of wave fronts at a plane boundary

SOLID LIQUID GAS

GLASS/PERSPEX WATER AIR

SLOWEST FASTEST

MOST DENSE

LEAST DENSE

AIR

GLASS/WATER

AIR

(LESS DENSE)

(MORE DENSE)

A When light travels from air into glass at an angle off the line of normal, (less dense to more dense), it slows down and bends towards the line of normal.

A

B

B When light travels from glass to air at an angle off the line of normal, (more dense to less dense), it speeds up and bends away from the line of normal.

C

D

C & D When light travels from air to glass or glass to air along the line of normal it does not change direction

What happens to light when it changes speed

(LESS DENSE)

More dense substance

(glass or water)

Less dense

substance

(air)

Refraction of wave fronts

Slow down – wavelength decreases

Speed up – wavelength increases

Glass/Water

More Dense

Air

Less Dense

Total Internal Reflection and Critical Angle

Angle less than

critical angle

(angle less than 42o)

Less dense (AIR)

More dense (GLASS)

Refracts out into air and bends

away from line of normal

boundary

Angle = critical angle

(Angle = 42o)

Less dense (AIR)

More dense (GLASS)

Travels along

boundary line

between air and glass

boundary

Angle more than critical angle

(Angle more than 42o)

Less dense (AIR)

More dense (GLASS)

Totally internally

reflected at same angle

back into glass

(boundary acts like a mirror)

boundary

Air

GlassAB

Angles A & B greater than critical angle of 42O

A

C

B

D

At A, B, C and D the angle is

greater than the critical angle so

the light gets totally internally

reflected

Fibre Optic Cable: used to send information as pulses of light

Glass

Protective Cladding

Outer Covering

A

B

CD

Air (less dense)

Air (less dense)

Glass (more dense)

At A, light enters glass, slows down and bends towards line of normal (refracts)

At B & C, angle greater than critical angle, light gets totally internally reflected

At D, angle less than critical angle so light leaves glass, speeds up and bends away from line of normal (refracts)

Total Internal Reflection through a fibre optic cable