1.4 diffraction of waves

1.4 DIFFRACTION

www.myfunphysicsworld.blogspot.com

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

DIFFRACTION

The diffraction of water waves through an obstacle

Diffraction

The property of waves that bend/spread out after a gap, or an obstacles

ACTIVITY 1.4.1(page 20)

Wave bends around the obstacle.If the size of the obstacle is large, the effect of diffraction is less obvious

Wave spreads out and change to semicircular shape after passing through the gap//more diffracted

The diffracted waves are almost straight in shape,with only a slight curvature at the edges // less diffracted

ACTIVITY 1.4.1

Degree of diffraction is higher

Degree of diffraction is lower

What happen to λλ, f & v?, f & v?

λλ i = λλ d ; f i = f d ; vi = vdwww.myfunphysicsworld.blogspot.com

What change when waves diffracted?

1.Shape

2.direction

3. Amplitude

(decreases)www.myfunphysicsworld.blogspot.com

Exercise Practical Text Book

, Question 1-6

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 of the waves //more diffracted

2) What is the shape of the diffracted waves when straight waves enter a gap bigger than the wavelength?

*Gap smaller or equal to the wavelength will produce semicircular diffracted waves (more diffracted//higher degree of diffraction)

The diffracted waves are almost straight in shape with only a slight curvature at the edges

3) Is there any difference in the wavelength of the incidence wavefronts and the diffracted wavefronts?

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

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 wave because the radio waves’ wavelength is larger than the gap

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 around the hill (obstacle).

Quick review 1.4

• The wave will become semicircular if the gap is smaller than the wavelength

Length of the gap

wavelength Incidence wave

Diffracted wave

• same wavelength

• the same frequency.

• same speed.

• Decreasing amplitude

unchanged

Bends towardsnormal

decreases

unchanged

decreases

Spreads out &bends around

unchanged

unchangedwww.myfunphysicsworld.blogspot.

When a plane wave travels through two straight barriers which form a gap between them, some of the 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 unchanged

B. The wavelength of both diffracted waves and reflected waves decreases

C. The frequency of the diffracted waves decreases while that of reflected waves remain unchanged.

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 cm

B. The waves passes through an obstacle of length 2 cm

C. The waves passes through gap of 4 cm.D. The waves passes through gap of 1 cm

1.4 diffraction of waves

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