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# 1.4 Diffraction Of Waves

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### 1.4 Diffraction Of Waves

1. 1. 1.4 DIFFRACTION www.myfunphysicsworld.blogspot.com
2. 2. By the end of today’s lesson you should be able to…• Describe diffraction of waves in terms of wavelength, frequency, speed, direction of propagation, and shape of waves• Draw a diagram to show diffraction of waves www.myfunphysicsworld.blogspot.com
3. 3. DIFFRACTION www.myfunphysicsworld.blogspot.com
4. 4. DIFFRACTION www.myfunphysicsworld.blogspot.com
5. 5. The diffraction of water waves through an obstacle www.myfunphysicsworld.blogspot.com
6. 6. DiffractionThe property of waves that bend/spreadout after a gap, or an obstacles www.myfunphysicsworld.blogspot. com
7. 7. ACTIVITY 1.4.1(page 20)Wave bends around the Wave spreads out and The diffracted waves areobstacle. change to semicircular almost straight in shape,If the size of the obstacle shape after passing with only a slightis large, the effect of through the gap//more curvature at the edgesdiffraction is less diffracted // less diffractedobvious www.myfunphysicsworld.blogspot.com
8. 8. ACTIVITY 1.4.1Degree of Degree ofdiffraction is higher diffraction is lower www.myfunphysicsworld.blogspot.com
9. 9. www.myfunphysicsworld.blogspot.com
10. 10. What happen to λ, f & v?λi = λ d ; f i = f d ; vi = vd www.myfunphysicsworld.blogspot.com
11. 11. What change when waves diffracted? 1.Shape 3. Amplitude 2.direction (decreases) www.myfunphysicsworld.blogspot.com
12. 12. Exercise Practical Text BookPage 18, Question 1-6 www.myfunphysicsworld.blogspot.com
13. 13. Question..(practical book-page 18)1) How does the size of a barrier affect the diffraction of waves???The smaller the size of the barrier, the higher the degree of the diffraction ofthe waves //more diffracted www.myfunphysicsworld.blogspot.com
14. 14. Question..(practical book-page 18) 2) What is the shape of the diffracted waves when straight waves enter a gap bigger than the wavelength?The diffracted waves are almost straight inshape with only a slight curvature at the edges *Gap smaller or equal to the wavelength will produce semicircular diffracted waves (more diffracted//higher degree of diffraction) www.myfunphysicsworld.blogspot.com
15. 15. Question..(practical book-page 18)3) Is there any difference in the wavelength of the incidence wavefronts and the diffracted wavefronts?No www.myfunphysicsworld.blogspot.com
16. 16. Question..(practical book-page 18)4) What can you predict the frequency of the incident waves and diffracted waves?No change.Frequency of the incident waves and diffractedwaves are the same www.myfunphysicsworld.blogspot.com
17. 17. Question..(practical book-page 18)5) A radio waves passes through an opening of 20 cm. What do you expect the shape of the diffracted wave to be? (the wavelength of radio wave is longer than 20 cm : x 103 m)Semi circular diffracted wavebecause the radio waves’ wavelength islarger than the gap www.myfunphysicsworld.blogspot.com
18. 18. Question..(practical book-page 18)6) In Penang, the Radio Broadcasting station is located in Bukit Gelugor. Residents in Balik Pulau are living on the other side of the hill. Explain how the radio receivers in Balik Pulau can receive radio broadcasting from Bukit Gelugor.The waves are diffracted.The waves bends aroundthe hill (obstacle). www.myfunphysicsworld.blogspot.com
19. 19. Quick review 1.4 Diffracted wave Length of the gapwavelength Incidence wave• The wave will become semicircular if the gap is smaller than the wavelength www.myfunphysicsworld.blogspot. com
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21. 21. • same wavelength• the same frequency.• same speed.• Decreasing amplitude www.myfunphysicsworld.blogspot.com
22. 22. www.myfunphysicsworld.blogspot.com
23. 23. www.myfunphysicsworld.blogspot.com
24. 24. www.myfunphysicsworld.blogspot.com
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26. 26. Bends towards Spreads out & r=i normal bends aroundunchanged decreases unchangedunchanged unchanged unchangedunchanged decreases unchanged www.myfunphysicsworld.blogspot. com
27. 27. When a plane wave travels through two straightbarriers which form a gap between them, some ofthe water are diffracted while some are reflected.Which of the following are correct?A. The wavelength and the speed of both diffracted waves and reflected waves remain unchangedB. The wavelength of both diffracted waves and reflected waves decreasesC. The frequency of the diffracted waves decreases while that of reflected waves remain unchanged. www.myfunphysicsworld.blogspot.com
28. 28. Which of following settings in a ripple tank produces the most prominent diffraction of a water wave of wavelength 2 cm?A. The waves passes through an obstacle of length 4 cmB. The waves passes through an obstacle of length 2 cmC. The waves passes through gap of 4 cm.D. The waves passes through gap of 1 cm www.myfunphysicsworld.blogspot.com