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1.3 ANALYSING REFRACTION OF WAVES a) Refraction of water waves, b) Refraction of light waves, c) Refraction of sound waves. Introduction : 1. Refraction of waves ; - “ When a wave traveling in one medium crosses the boundary into a

medium where its velocity is different, the transmitted wave may move in a different direction than the incident wave.”

2. Effect of refraction of waves ;

a) Refraction of water waves : 1.“ when a water wave travelling from deep area to shallow area.”

Ripple tank

v, (velocity) will change after refraction. f, (frequency) same before and after refraction. .will change after refraction (wavelength) ,ג

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2. The characteristics of the refracted of water waves are as below ;

shallow ג < deep ג גf same before and after refraction ( f = constant ), v v deep > v shallow

Deep area Refractred near to normal line. (angle of i ≠ 0 ) Shallow area Refracted far from normal line. ( i ≠ 0) f = constant f = v / ג

v1 / 1 ג = v2 / 2ג

3. A pattern of refraction of water waves. - different types of transparent plate/perspecs plate.

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b) Refraction of light waves :

1. “When a light wave travelling in one medium crosses the boundary into a medium with different density where it velocity is different.”

2. v = at low density medium. 3. v = at high density medium.

4. Example of refraction of light wave ,

c) Refraction of sound waves :

1. Sound waves travel faster in warm air than in cool air. 2. On a hot day :

The hot surface of the earth causes the layer of air near the surface to be warmer. This causes sound waves to be refracted away from the earth.

On a cool night : The sound waves travel slower in the cooler layer of air near the surface of the earth than in the upper, warmer air. As a result, the waves are refracted towards the earth.

3. This explains why sound can be heard over a longer distance on a cold night compared with a hot day as illustrated as figure below.

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ACTIVITIES : (50 MINUTES) 1. A water waves travelling from shallow area to deep area with v = 25 cm/s and 30

cm/s. Find the ratio of wavelength from shallow area to deep area. ( 2 ג : 1ג )

2. Draw a pattern of refraction of water waves from shallow area to deep area.

3. When a light wave traveling in one medium crosses the boundary into a medium

with ______________________ where it _______________ is different. 4. Velocity is _____________ at low density medium and velocity is _____________ at high density medium. 5. Sound wave travel _________ in warm air than in cool air. 6. What happen to sound wave on a hot day ? ________________________________________________________________ ________________________________________________________________ 7. What happen to sound wave on a cool day ? ________________________________________________________________ ________________________________________________________________ 8. What is the effect of refraction of waves to ……

v, (velocity) f, (frequency) (wavelength) ,ג

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ASSESTMENT (40 MINUTES) (Objective questions )

1. Refraction of water wave is defined as

A. when a water wave travelling from deep area to shallow area.

B. waves spread as they travel and when they encounter obstacles or slits they bend around it and pass into the region.

C. when a wave travelling in one medium crosses the boundary into a medium with different density where it velocity is different.

2. Refraction of light wave is defined as

A. waves spread as they travel and when they encounter obstacles or slits they bend around it and pass into the region.

B. when a wave travelling in one medium crosses the boundary into a medium with different density where it velocity is different.

C when a wave travelling from deep area to shallow area

3. Effect of refraction of waves are as below except

A. velocity will change after refraction.

B. frequancy same before and after refraction.

C. wavelength same after refraction.

D.wavelength will change after refraction.

4. An audio signal generator produces sound with constant speed. When the frequency of the sound increases, its wavelength .. A. decreases B. increases C. remains constant

5. Sound waves travel _______ in warm air than in cool air.

A. Very slow B. Slow

C. Same D. Faster

6. What happen to sound wave on a hot day ?

A. Remains constant.

B. Effect to human body.

C. Sound waves are refracted towards the earth.

D. Sound waves to be refracted away from the earth.

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(Structure question) 1. Complete the diagrams as below by drawing the wavefronts to show the

refraction of water waves.

2. Water waves undergo refraction when moving from a deep area to a shallow

area. Make a comparison between incident waves and refracted waves in terms of

(a) wavelength, (b) frequency, (c) speed, (d) direction of propagation.

3. In figure above, a plane wave with frequency 4 Hz and velocity 8 cms1

travelling from shallow area to deep area. Find the wavelength in (a) shallow area and (b) deep area.

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ANSWER KEY.

(Activity)

1. 5 : 6 2.

(3 ~ 8) Please refer to note.

ANSWER KEY. (Assesment) Objective questions.

1. A 2. B 3. C 4. A 5. D 6. D

Structured Question.

1. Please refer to note. 2.

Effects Incident waves Refracted waves increase decrease גf remain contants remain contants v increase decrease

direction same direction with incident waves.

change direction

3.Guna formula : v = f ג cetek = 2 cm ג dalam = 2.5 cm ג