1.4 Diffraction Of Waves

1.4 DIFFRACTION

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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

DIFFRACTION


The diffraction of water waves
through an obstacle


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

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ACTIVITY 1.4.1(page 20)

Wave bends around the Wave spreads out and The diffracted waves are
obstacle. change to semicircular almost straight in shape,
If the size of the obstacle shape after passing with only a slight
is large, the effect of through the gap//more curvature at the edges
diffraction is less diffracted // less diffracted
obvious

ACTIVITY 1.4.1

Degree of Degree of
diffraction is higher diffraction is lower

What happen to λ, f & v?

λi = λ d ; f i = f d ; vi = vd

What change when waves diffracted?

1.Shape 3. Amplitude
2.direction (decreases)

Exercise
Practical Text Book
Page 18, 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?

The diffracted waves are almost straight in
shape 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)

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

No


4) What can you predict the frequency of the
incident waves and diffracted waves?

No change.
Frequency of the incident waves and diffracted
waves 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

Diffracted
wave
Length of the gap

wavelength Incidence
wave

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

• same wavelength
• the same frequency.
• same speed.
• Decreasing amplitude


Bends towards Spreads out &
r=i normal bends around

unchanged decreases unchanged

unchanged unchanged unchanged

unchanged decreases unchanged
com

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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