# Case Study Questions for Class 12 Physics Chapter 10 Wave Optics

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Case Study Questions for Class 12 Physics Chapter 10 Wave Optics

Question 1:

Diffraction of Light:
A and B went to purchase a ticket of a music programme. But unfortunately only one ticket was left. They purchased the single ticket and decided that A would be in the hall during the 1st half and B during the 2nd half.
Both of them reached the hall together. A entered the hall and found that the seat was behind a pillar which creates an obstacle. He was disappointed. He thought that he would not be able to hear the programme properly.

B was waiting outside the closed door. The door was not fully closed. There was a little opening. But surprisingly, A could hear the music programme.
This happened due to diffraction of sound.
The fact we hear sounds around corners and around barriers involves both diffraction and reflection of sound.

Diffraction in such cases helps the sound to “bend around” the obstacles.
In fact, diffraction is more pronounced with longer wavelengths implies that we can hear low frequencies around obstacles better than high frequencies.

B was outside the door. He could also hear the programme. But he noticed that when the door opening is comparatively less he could hear the programme even being little away from the door. This is because when the width of the opening is larger than the wavelength of the wave passing through the gap then it does not spread out much on the other side. But when the opening is smaller than the wavelength more diffraction occurs and the waves spread out greatly – with semicircular wavefront. The opening in this case functions as a localized source of sound.

(i) A and B could hear the music programme due to phenomenon named
(a) interference.
(b) scattering
(c) diffraction.
(d) dispersion

Option (c) is correct.
Explanation: The fact we hear sounds around corners and around barriers involves both diffraction and reflection of sound.

(ii) Diffraction is more pronounced with ______ wavelengths.
(a) Longer
(b) Shorter
(c) fluctuating
(d) all

Option (a) is correct.
Explanation: In fact, diffraction is more pronounced with longer wavelengths

(iii) The minimum and maximum frequencies in the musical programme were 550 Hz and 10 kHz. Which frequency was better audible around the pillar obstacle?
(a) 10 kHz
(b) 550 kHz
(c) Mid frequency
(d) The complete frequency range

Option (a) is correct.
Explanation: In fact, diffraction is more pronounced with longer wavelengths implies that you can hear low frequencies around obstacles better than high frequencies.

(iv) Diffraction of sound takes place more when :
(a) sound is diffracted through an opening having width equal to the wavelength of the sound.(b) sound is diffracted through an opening having width more than the wavelength of the sound.
(c) sound is diffracted through an opening having width less than the wavelength of the sound.
(d) diffraction of sound does not depend on the width of the opening.