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# Assertion & Reason Test: Wave Optics

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## 18 Questions MCQ Test Physics Class 12 | Assertion & Reason Test: Wave Optics

Assertion & Reason Test: Wave Optics for NEET 2023 is part of Physics Class 12 preparation. The Assertion & Reason Test: Wave Optics questions and answers have been prepared according to the NEET exam syllabus.The Assertion & Reason Test: Wave Optics MCQs are made for NEET 2023 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Assertion & Reason Test: Wave Optics below.
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Assertion & Reason Test: Wave Optics - Question 1

### Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.Assertion (A): Wavefront emitted by a point source of light in an isotropic medium is spherical.Reason (R): Isotropic medium has the same refractive index in all directions.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 1 If a medium has the same refractive index at every point in all directions, then the waveform obtained from a point source in such a medium is spherical since the wave travels in all directions at the same speed. Such a medium is known as isotropic medium. So, the assertion and reason both are true and the reason explain the assertion properly.
Assertion & Reason Test: Wave Optics - Question 2

### Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.Assertion (A): No interference pattern is detected when two coherent sources are too close to each other.Reason (R): The fringe width is inversely proportional to the distance between the two slits.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 2 No interference pattern is detected when two coherent sources are too close to each other. The assertion is true.

Fringe width is proportional to 1/d. When d becomes too small, the fringe width becomes too large. So no pattern will be visible. So, the reason is also true. Reason also explains the assertion.

Assertion & Reason Test: Wave Optics - Question 3

### Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.Assertion (A): Fringes of interference pattern produced by blue light are narrower than that produced by red light.Reason (R): In Young’s double slit experiment, fringe width= λD/d

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 3 Fringes of interference pattern produced by blue light are narrower than that produced by red light. The assertion is true.

Fringe width = λD/d. Since blue light has a wavelength smaller than that of red light, blue light produces narrower fringes. So, reason is also true and explains the assertion.

Assertion & Reason Test: Wave Optics - Question 4

Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.

Assertion (A): According to Huygens theory no back-ward wavefront is possible.

Reason (R): Amplitude of secondary wavelets is proportional to (1+ cos q), where q is the angle between the ray at the point of consideration and direction of secondary wavelet.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 4 According to Huygens theory each and every point on a wavefront is the source of secondary wavelets. Secondary wavelets do not proceed backward. So the assertion is true.

Kirchhoff’s explained that amplitude of secondary wavelets is proportional to (1+ cos q), where q is the angle between the ray at the point of consideration and direction of secondary wavelets. In the backward direction q = 180°; so 1 + cos q = 0; so their secondary wavelets do not proceed backward.

Hence assertion and both are true and the reason properly explains the assertion.

Assertion & Reason Test: Wave Optics - Question 5

Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.

Assertion (A): When a light wave travels from rarer to denser medium, its speed decreases. Due to this reduction of speed the energy carried by the light wave reduces.

Reason (R): Energy of the wave is proportional to the frequency.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 5 When a light wave travels from rarer to denser medium, its speed decreases. But this reduction of speed does not imply the loss of energy carried by the light wave. So the assertion is false.

Energy of a wave is proportional to the frequency of the wave which remains the same in every medium. Hence there is no loss of energy. So, the reason is true.

Assertion & Reason Test: Wave Optics - Question 6

Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.

Assertion (A): For best contrast between maxima and minima in the interference pattern of Young’s double slit experiment, the amplitudes of light waves emerging from the two sources should be equal.

Reason (R): For interference, the sources must be coherent.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 6 For destructive interference, a = a1 ~ a2. When a1 = a2, only the minima will be completely dark. This will create the best contrast. So the assertion is true.

For interference, the sources must be coherent. Reason is also true. But the reason does not explain the assertion.

Assertion & Reason Test: Wave Optics - Question 7

Directions : In the following questions, A statement of Assertion(A) is followed by a statement of Reason (R). Mark the correct choice as.

Assertion (A): Diffraction takes place with all types of waves.

Reason (R): Diffraction is perceptible when the wavelength of the wave is comparable to the dimension of the diffracting device.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 7 Diffraction is the spreading of waves around obstacles. It takes place with all types of waves (mechanical, non-mechanical, transverse, longitudinal) and with very small moving particles (atom, neutron, electron etc.) which show wave-like properties. So, the assertion is true. Diffraction is perceptible when the wavelength of the wave is comparable to the dimension of the diffracting device. The reason is also true. But it does not explain the assertion.
Assertion & Reason Test: Wave Optics - Question 8

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : Thin film such as soap bubbles or a thin layer of oil on water show beautiful colours when illuminated by white light.

Reason : It happens due to the interference of light reflected from the upper and lower face of the thin film.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 8 When white light is incident on thin film, the film appears coloured. These colours are due to the interference between light waves reflected from the top and bottom surfaces of thin films. The colour depends on the thickness of the film and also the angle of incidence of the light.
Assertion & Reason Test: Wave Optics - Question 9

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : It is necessary to have two waves of equal intensity to study interference patterns.

Reason : There will be an effect on clarity if the waves are of unequal intensity.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 9 For interference, the waves may be of unequal intensities.
Assertion & Reason Test: Wave Optics - Question 10

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : In YDSE, if a thin film is introduced in front of the upper slit, then the fringe pattern shifts in the downward direction.

Reason : In YDSE if the slit widths are unequal, the minima will be completely dark.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 10 If a film is introduced in the upper slit, the optical path traveled by ray from upper source is more and that traveled by that from lower source, hence some finite path difference exists at the point of earlier central maxima(point equidistant from both sources). Now to compensate for this extra path difference, ray from the upper source needs to travel less than ray from lower source. So the central maxima would now be obtained at a point of screen that is closer to the upper source. Hence central maxima shifts upwards, so does the pattern. If slit widths are different, intensity of light from both the sources is different. So the minima will have intensity (I1 ​− I2)2 > 0.

So the minima would not be dark. Therefore both the assertion and reason are incorrect.

Assertion & Reason Test: Wave Optics - Question 11

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : In YDSE number of bright fringe or dark fringe can not be unlimited

Reason : In YDSE path difference between the superposing waves can not be more than the distance between the slits.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 11 Path difference at a point of superposition on the screen at a distance 'y' from the central maxima in YDSE is given by yd/D. Thus y can be any large to form any order of bright or dark fringe. Apparently from the expression of path difference, it can be more than d for large values of y.
Assertion & Reason Test: Wave Optics - Question 12

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : Coloured spectrum is seen when we look through a muslin cloth.

Reason : It is due to the diffraction of white light on passing through fine slits.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 12 When we look through a muslin cloth coloured spectrum cab be seen. Because muslin cloth has fine slits in it. When white light passes through thin fine slits, diffraction occurs. Due to this diffraction of light we can coloured spectrum.
Assertion & Reason Test: Wave Optics - Question 13

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : According to Huygen’s principle, no backward wave-front is possible.

Reason : Amplitude of secondary wavelet is proportional to (1 + cos θ) where θ is the angle between the ray at the point of consideration and the direction of secondary wavelet.

Assertion & Reason Test: Wave Optics - Question 14

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : No interference pattern is detected when two coherent sources are infinitely close to each other.

Reason : The fringe width is inversely proportional to the distance between the two sources.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 14 When d is negligibly small, fringe width. β which is proportional to 1/d may become too large. Even a single fringe may occupy the whole screen. Hence the pattern cannot be detected.
Assertion & Reason Test: Wave Optics - Question 15

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : White light falls on a double slit with one slit is covered by a green filter. The bright fringes observed are of green colour.

Reason : The fringes observed are coloured.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 15 Interference will take place in green light only
Assertion & Reason Test: Wave Optics - Question 16

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : In Young’s double slit experiment if wavelength of incident monochromatic light is just doubled, the number of bright fringes on the screen will increase.

Reason : Maximum number of bright fringe on the screen is inversely proportional to the wavelength of light used

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 16 Wavelength is inversely proportional to the number of fringes, hence by doubling the wavelength the number of fringes decreases. Hence Assertion and reason are false.
Assertion & Reason Test: Wave Optics - Question 17

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : Interference pattern is made by using yellow light instead of red light, the fringes become narrower.

Reason : In YDSE, fringe width is given by β=λD/d

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 17 The fringe width is given by

β=λD/d

The fringe width is directly proportional to the wavelength.

The wavelength of blue light is less than that of the red light. So, for blue light the fringe will be narrower.

So, Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Assertion & Reason Test: Wave Optics - Question 18

Directions: These questions consist of two statements, each printed as Assertion and Reason. While answering these questions, you are required to choose any one of the following four responses.

Assertion : Diffraction takes place for all types of waves mechanical or nonmechanical, transverse or longitudinal.

Reason : Diffraction’s effects are perceptible only if wavelength of wave is comparable to dimensions of diffracting device.

Detailed Solution for Assertion & Reason Test: Wave Optics - Question 18 Diffraction is defined as the bending of light around the corners of the obstacle or aperture into the region Of geometrical shadow if the obstacle. Diffraction occurs with all waves, including sound waves, water waves and electromagnetic waves.

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