Explore topic-wise InterviewSolutions in .

The correct answer is (b) False

For explanation I would SAY: Two independent sources of light cannot be COHERENT. This is because the light is EMITTED by INDIVIDUAL atoms when they return to the ground STATE. Even the smallest source of light contains billions of atoms which obviously cannot emit light waves in the same phase.

The CORRECT choice is (d) 0^o

Best explanation: When a wave undergoes REFRACTION, the PHASE change will be zero. The phase change is what guides the process. Therefore, no phase change occurs to a wave during refraction.

The correct choice is (B) 443 NM

The EXPLANATION: λ = 589 nm, μ = 1.33.

Wavelength in water, λW = \(\frac {\lambda }{\mu }\)

λW = \(\frac {589}{1.33}\)

λW = 443 nm.

Correct choice is (B) 1.5

For EXPLANATION I WOULD say: OPTICAL path = μ × Path in medium.

The optical path for GLASS = Optical path for water.

μg = \(\frac {(1.33 \times 2.25)}{(2.0)}\)

μg = 1.50.

Correct OPTION is (b) Plane of rotation

To explain: Plane of vibration, the plane of POLARIZATION, and DIRECTION of propagation of the LIGHT wave are mutually perpendicular to the polarized light wave in a plane. The other factors are not mutually perpendicular to the polarized light wave in a plane.

Right OPTION is (a) 0.5 mm

Best EXPLANATION: Fringe width is given as:

β = \(\frac {D\lambda }{d}\).

So β = \(\frac { (1 \TIMES 500 \times 10^{-9} ) }{(10^{-3})}\)

β = 0.5 mm

Therefore, the fringe separation when blue-green light of wavelength 500 nm is used is 0.5 mm.

Right option is (C) Increases

For EXPLANATION I WOULD SAY: Fringe width is given as:

 β = \(\frac {D\lambda }{d}\)

As the SCREEN is moved closer to the two slits, the distance denoted by D decreases and so fringe width β increase.

Right ANSWER is (C) π radian

The best EXPLANATION: When a wave is reflected in the rarer medium from the surface of a denser medium, it UNDERGOES a PHASE change of π radian. Therefore, when a wave undergoes reflection at a denser medium, the phase change will be π radian.

Right option is (c) Disappears

Explanation: The positions of bright and DARK fringes will change rapidly. Such rapid changes cannot be detected by our eyes. Uniform ILLUMINATION is SEEN on the SCREEN i.e., the INTERFERENCE pattern disappears.

Correct answer is (b) False

To elaborate: In Huygens’ THEORY, LIGHT waves are LONGITUDINAL and REQUIRE a material MEDIUM for their propagation. That is why, Huygens’ assumed the existence of an all-pervading hypothetical medium, called ether.

The CORRECT choice is (b) False

Easiest explanation: As the wavelength of light is much SMALLER than the size of the OBJECTS around us, so diffraction of light is not easily seen. Therefore, for diffraction of a wave, an obstacle or aperture of the size of the wavelength of light of the wave is needed. As the wavelength of light is of the ORDER of 10-6m and \(\FRAC {obstacle}{aperture}\) of this size are rare, diffraction is not common in light waves.

Right option is (c) ELECTRIC field vector

For explanation I would say: An electric field vector is used to represent the POLARIZATION of an EM WAVE. It is perpendicular to the plane of propagation of the light wave. Therefore, a vertically polarized electromagnetic wave of wavelength λ has its electric field vector OSCILLATING in the vertical direction.

Correct choice is (d) Bright

Explanation: Waves from the distant source are diffracted by the edge of the disc. These diffracted waves INTERFERE constructively at the CENTER of the SHADOW and PRODUCE a bright fringe. Therefore, the nature of the fringe produced is bright.

Right choice is (b) 33.7^o

To explain: As ip + RP = 90^o

rp = 90^o – 63.8^o

rp = 26.2^o

Therefore, the angle of REFRACTION in the GLASS is 26.2^o.

Correct OPTION is (C) 1.95 × 10^8 m/s

Easiest explanation: \( \FRAC {v_g}{v_w} = \frac {\mu_w}{\mu_g}\)

Vg = \((\frac {\mu_w}{\mu_g})\) × VW

\(\frac {v_g}{v_w} = ( \frac {1.3}{1.5} ) \) × 2.25 × 10^8

\(\frac {v_g}{v_w}\) = 1.95 × 10^8 m/s.

Right choice is (a) The PLANE containing the direction of propagation of light

Easy explanation: The plane containing the direction of propagation of light and perpendicular to the plane of VIBRATION is called the plane of polarization. It contains no VIBRATIONS. POLARIZED light waves are light waves in which the vibrations OCCUR in a single plane.

Right OPTION is (a) Coherent sources

The best I can explain: Coherent light is a form of light WHOSE photons share the same FREQUENCY and whose wavelengths are in phase with one another. The phase difference between the waves should be CONSTANT in case of coherent sources.

Right answer is (b) Remains unchanged

To explain: The frequency of the wave remains unchanged. This is because the frequency is INDEPENDENT of the wave DYNAMICS. Therefore, when a LIGHT wave enters from the AIR MEDIUM into the glass medium, the frequency will be the same.

The correct choice is (c) Transverse

Easiest explanation: Only transverse WAVES SHOW the property of polarization. Their vibrations can occur in all directions PERPENDICULAR to the direction of TRAVEL. The LONGITUDINAL, infrared, and microwaves do not show the property of polarization.

Correct answer is (a) 4 I’

Explanation: Resultant intensity at the point of CONSTRUCTIVE INTERFERENCE is GIVEN as FOLLOWS:

I = I’ + I’ + 2√I’I’ cos 0^o

I = 4 I^‘

Therefore, the value of the resultant intensity at a point of constructive interference is 4 I’.

Right choice is (b) False

The explanation: Unlike TRANSVERSE WAVES such as electromagnetic waves, longitudinal waves such as sound waves cannot be polarized. This is because, sound waves vibrate along their direction of PROPAGATION, and thus, cannot be polarized.

The correct choice is (c) INCREASES FOUR times

The explanation: Original FRINGE width is given as ➔ β = \(\frac {D\lambda }{d}\).

So, the NEW fringe width is ➔ β’ = \(\frac {\lambda.2D}{ ( \frac {d}{2} ) }\)

β’ = 4β

Therefore, the new fringe width is 4 β.

The CORRECT CHOICE is (c) 1.25

Easy explanation: μ = \(\frac {c}{v_t}\)

μ = 3 × \(\frac {10^8}{2.4}\) × 10^8

μ = 1.25

Correct option is (b) Interference of secondary WAVELETS

For explanation: Diffraction occurs DUE to interference of secondary wavelets between different portions of a wavefront allowed to pass across a small aperture or OBSTACLE. Interference can be either constructive or destructive. When interference is constructive, the INTENSITY of the wave will increase.

The correct choice is (C) DECREASES

For EXPLANATION: Wavelength of LIGHT in water decreases, so the width of the central maximum also decreases. This is the impact on the width of the central maximum when a single slit is completely immersed in water.

The CORRECT answer is (d) zero

Best explanation: Resultant intensity at the point of DESTRUCTIVE interference will be as follows:

I = I0 + I0 + 2√I0 I0 COS 180^o

I = 0

Therefore, the VALUE of the resultant intensity at a point of destructive interference is zero.

Correct ANSWER is (c) LASER

To explain: LASER is the SHORT form for Laser Amplification by Stimulated EMISSION RADIATION. The amplified light beam coming out of a LASER is essentially due to the emission of electrons stimulated by incident radiation consisting of photons. As a result, this causes the coherent BEHAVIOR of the LASER beam.

The correct answer is (a) True

Easy explanation: Yes, the scattering of waves can be COHERENT and INCOHERENT. The scattering of a wave is coherent and constructive if the phase delay is the same for all the scattered waves. If it VARIES randomly, then it is CONSIDERED to be incoherent.

The correct answer is (b) When the paths taken by all of the interfering waves are lesser than the COHERENCE LENGTH

Explanation: Coherence length is defined as the propagation DISTANCE over which a COHERENT wave maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves are lesser than the coherence length.

Right choice is (d) POLAROIDS

For explanation I would say: Polaroids absorb only that part of the light which produces a dazzling effect in the EYE. But colored glasses absorb more light incident on them and so the image appears DIM. Therefore, SUNGLASSES are made of Polaroids.

The CORRECT OPTION is (a) 1.25

The explanation is: μ1 = \(\frac {c}{v_1}\)

μ1 = \(\frac {(3 \TIMES 10^8)}{(2.4 \times 10^8) }\)

μ1 = 1.25.

Correct answer is (d) They TWO LIGHT sources should be NARROW

The best explanation: The essential conditions for two light waves to be coherent includes that the two waves must be continuous, the two waves should be of the same frequency or wavelength, and they should have a constant or zero phases difference. So, the unnecessary CONDITION for two light waves to be coherent is the statement that the sources should be narrow.

The correct option is (C) The size of the aperture MUST be COMPARABLE to the wavelength of light

Easiest explanation: Diffraction is the SPREADING out of waves as they pass through an aperture or around objects. The diffraction of light OCCURS when the size of the obstacle or the aperture is comparable to the wavelength of light.

Right choice is (b) FALSE

For explanation: No, this STATEMENT is false. If they intersect, then there will be two rays or two directions of propagation of energy at the point of INTERSECTION which is not possible. THEREFORE, two wave-fronts do not intersect with each other.

Right option is (b) 30^o

Explanation: Half angular width of the CENTRAL maximum is given by:

Sin θ = \(\frac {\lambda }{d}\)

Sin θ =\(\frac {1000 \TIMES 10^{-9}}{2 \times 10^{-6}}\)

Sin θ = 0.5.

Θ = 30^o

The correct CHOICE is (b) Increases

To explain I would say: Fringe width is EXPRESSED as:

β = \(\FRAC {D\lambda }{d}\).

So, as the separation (d) between the two slits decreases, the fringe width increases. They are inversely PROPORTIONAL to each other.

The CORRECT option is (b) βO < βY < βG

To explain: Fringe WIDTH is EXPRESSED as:

β = \(\FRAC {D\lambda }{d}\).

Since the wavelength are related as shown ➔ λG < λY < λO, we can say that ➔ βG < βY < βO.

Correct answer is (c) Amplitude

Easy EXPLANATION: Coherent waves are the waves with the same frequency and the wavelength of the waves are in phase as well. Therefore, the phase DIFFERENCE is CONSTANT. But the coherent waves do not have the same amplitude. Since the amplitude is different, there will be no complete constructive interference where they meet, so they will contribute POORLY to an interference PATTERN.

Correct OPTION is (c) Reflection

Easy explanation: Light undergoes interference, diffraction, and polarization. These phenomena ESTABLISH that light is a wave MOTION. THEREFORE, out of the options, reflection isn’t a SUITABLE phenomenon to establish that light is wave motion.