LEARNING OUTCOMESDescribe refraction of waves in terms of

the angle of incidence, angle ofthe angle of incidence, angle ofrefraction, wavelength, frequency, speedand direction of propagations

Draw a diagram to show refraction ofwaves.

In deep sea regions, the water waves takethe shape of plane waves.

This is because the depth of the waterare almost the same

As the waves approach the shore, theybend according to the shape of theshoreline.shoreline.

Why ?

What happens to waves as theypropagate in different depths of water?

A square glass slab is placed in the rippletank so as to create different depths ofwater.

What can you say about the wavelengthsof the waves as the waves propagate indifferent depths of water?

When waves propagate from the deep tothe shallow regions, the wavelengthdecreases.

What happens to the frequency of thewaves?

As the waves are continuously producedby the same source, the frequency of thewaves remains constant.waves remains constant.

What happens to velocity of the waves asit travels in two different depth of water?

v = fλ

Sine f is constant and λ decreases in shallowregion.region.

Thus v decreases in shallow region.

The speed of the waves depends on thedepth of water.

The ripples slow down as they pass throughshallow water regions.

This causes the wavelength to decrease.

As the waves propagate from the shallowto the deep water regions, thewavelength increases.

What can you say about the direction ofthe waves as they propagate in differentdepths of water?

As waves propagate of an angle to waterof different depths, there is a change indirection of the waves.

When waves propagate from water ofdifferent depths, there is a change inwavelength, speed and direction of thewaves.

The change in direction is due to thechange in speed of the waves. Thisphenomenon is called Refraction.

What is Refraction of Waves?Refraction of waves is a change of

direction in the propagation of wavesfrom one medium to another due to afrom one medium to another due to achange of speed.

Refraction of water waves is a change indirection as the water waves propagatein different depths of water due to achange of speed

What happens to frequency,speed, wavelength & direction?

The frequency of the waves is equal tothe frequency of the source of vibrationand hence it remains unchanged.and hence it remains unchanged.

But the speed, wavelength and directionof propagation change.

The relationship between v and λ of a water wave in deep and shallow water:

v = fλ f is constant

v is directly proportional to λ

vvv

2

2

1

1tan

vvtcons

vf

How does the direction of wavechanges when refraction occurs?

How does the direction of wavechanges when refraction occurs?

Draw a diagram to showrefraction of wavesrefraction of waves

1. Draw a boundary line to separate deepand shallow regions. Label the region.

2. Draw a line to represent the directionof propagation of incident waves. Markwith an arrow. Label O at the pointwhere this line meets the boundary.

3. Draw the normal line at point O.

4. From point O, draw a line to represent thedirection of propagation of refractedwaves. Mark with an arrow. When wavespropagate from deep to shallow regions,the refracted waves bend towards thenormal.

5. Draw the normal line at point P.

6. From point P, draw a line to represent thedirection of refracted waves. When wavespropagate from the shallow to the deepregions, the refracted wave bends awayfrom the normal line. Mark with an arrow.

7. Draw the wavefronts which areperpendicular to the direction ofincident and refracted waves.

8. Make sure the wavelength in deepregions is bigger than in the shallowregions.

Activity 2: To study the refractionof water in a ripple tank

Use a ripple tankto producestraight waves.

Place a piece ofPlace a piece ofglass plate in thewater to create ashallow region.

Observe thewaves.

Discussion

1. Compare the wavelength for the water wavein the deep region and the shallow region.

The wavelength for the water in the deepregion is greater.

2.Compare the frequency of the water wavein the deep region and the shallow region.

Frequency of the water wave in the deepregion and the shallow region are equal.

3. By using the answer in question 1 & 2, andformula v = fλ, compare the speed of the waterwaves in the two regions.

v is directly proportional to λ when f is constant. So the speed of the water waves in the deepregion is greater than in the shallow region.

Discussion

region is greater than in the shallow region.

4.How does the direction of waves change whenpassing from the deep region to the shallowregion?

The water waves will be refracted toward thenormal line.

5.When waves pass from the deep regionto the shallow region, how do thefollowing properties of the wave change?

Discussion

Direction: refracted toward the normalline

Wavelength: decreases

Speed: decreases

Refraction of water waves occurs whenthe wave pass from deep region to theshallow region due to the change of the

Conclusion

shallow region due to the change of thevelocity of the water waves.

18 / 3 = v/1.5

V = 9.0 cm/s

Application of refraction of wavesThe wave front of sea water will follow

the shape of the shore when itapproaches the shore

Application of refraction of waves

The water in the bay is calm compared tothe water at the cape.

It is because the depth of water variesslowly across the area of the bay and theenergy of the water wave spreads to aenergy of the water wave spreads to awider area compared to the region nearthe cape.

The amplitude of the water wave nearthe bay is low and hence the water at thebay is calm.

Refraction of sound waves

Sound waves travels faster in warm air than coldair.

On a hot day, the hot surface of the Earth causesthe layer of air near the surface to be warmer.

This causes sound waves to be refracted awayfrom the earth

Refraction of sound waves

On a cool night, the sound waves travelslower in the colder layer of the air near thesurface of the earth than in the upper layer.

The waves are refracted towards the earth.

Hence sound can be heard over a longerdistance and clearer on a cold nightcompared to a hot day.

Refraction of sound waves

compared to a hot day.

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