1.4 Diffraction Of Waves

1.4 ANALYSING DIFFRACTION OF WAVES a) Diffraction of water waves, b) Diffraction of light waves, c) Diffraction of sound waves. Introduction : 1. Diffraction of waves ; - “ Waves spread as they travel, and when they encounter obstacles or slits they bend around it and pass into the region.”

2. Effect of diffraction of waves ; Speed f ‫ג‬ Amplitude

does not change does not change does not change decreases

a) Diffraction of water waves :

Ripple tank -1-

1. Slits

i) Slit size ≈ ‫ג‬ ii) The degree of diffraction is larger.

i) Slit size > ‫ג‬ ii)The degree of diffraction is smaller.

2. a) Obstacle

2

i) Obstacle size ≈ ‫ג‬ ii) The degree of diffraction is larger.

ii) Obstacle size > ‫ג‬ ii)The degree of diffraction is smaller.

b) Round obstacle

i) The degree of diffraction is larger.

b) Diffraction of light waves :

c) Diffraction of sound waves :

3

A student can hear the sound of radio beyond the wall.

ACTIVITIES : (50 MINUTES) 1. Diffraction of waves is waves spread as they travel and when they encounter ____________________ or ____________ they bend around around it and pass into the region. 2. Fill the blanks with does not change or decreases. Effect of diffraction of waves ; Speed f ‫ג‬ Amplitude 3. Draw a pattern of diffraction of waves :

ASSESTMENT (40 MINUTES)

4

(Objective questions ) 1.

Diffraction of waves 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. Waves disappear as they travel and when they encounter obstacles or slits.

2. What happen to speed when the water wave travelling through round obstacle ? A. small B. larger C. does not change D. decreases

C. Waves spread to two pattern of waves. D. Waves change to energy. 3.

4. What happen to the degree of diffraction when the slit size is bigger than wavelength ?

Effect of diffraction of waves are as below except .. A. speed is change.

A. smaller

B. frequency is change.

B. larger

C. wavelength does not change.

C. does not change

D. Amplitude is increase.

D. disappear 5.

6. A man can hear the sound of radio beyond the wall because of …

What happen to the degree of diffraction when the slit size is smaller than wavelength ?

A. Reflection of waves.

A. smaller

B. Refraction of waves.

B. larger

C. Diffraction of waves.

C. does not change

D. Inference of waves.

D. disappear

(Structure question)

5

1. Describe the diffraction of waves. ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ 2. State the degree of diffraction if ; a) obstacle size is decrease. ____________________ b) wavelength for incident wave is increase. ____________________ 3. Draw a pattern of diffraction of light wave ; a) smaller slit b) larger slit

4. Draw a pattern of diffraction of water wave ;

6

ANSWER KEY. (Activity) 1. Obstacles, slits 2. does not change does not change does not change decreases 3. Please refer to note.

ANSWER KEY. (Assesment) Objective questions. 1. A 2. B 3. C 4. A 5. B 6. C Structured Question 1. Please refer to note. 2. a) larger b) smaller 3.

7

Smaller slit

Larger slit

4.

8