CBSE Class 12 Physics Ray and Wave Optics Assignment

TEST SERIES(PHYSICS)

RAY AND WAVE OPTICS

Question. In Young's double slit experiment with sodium vapour lamp of wavelength 589 nm and the slits 0.589 mm apart, the half angular width of the central maximum is
(a) sin^–1 0.01
(b) sin^–10.0001
(c) sin^–1 0.001
(d) sin^–1 0.1

Answer: C

Question. The separation between successive fringes in a double slit arrangement is x. If the whole arrangement is dipped under water what will be the new fringe separation? [The wavelenght of light being used is 5000 Å]
(a) 1.5 x
(b) x
(c) 0.75 x
(d) 2 x

Answer: C

Question. When the angle of incidence is 60° on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is
(a) √2 x 10⁸ms^-1
(b) √3 x 10⁸ms^-1
(c) 2 x 10⁸ms^-1
(d) 3 x 10⁸ms-1

Answer: B

Question. Young's double slit experment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly 
(a) 1.59
(b) 1.69
(c) 1.78
(d) 1.25

Answer: C

Question. A ray of light is incident on the surface of a glass plate at an angle of incidence equal to Brewster’s angel f. If m represents the refractive index of glass with respect to air, then the angle between the reflected and the refracted rays is
(a) 90° + Φ
(b) sin^–1(m cos Φ)
(c) 90º
(d) 90º sin^-1(sin Φ/μ)

Answer: C

Question. A rocket is receding away from earth with velocity 0.2 c. The rocket emits signal of frequency 4 × 10⁷ Hz. The apparent frequency observed by the observer on earth will be
(a) 4 × 10⁶ Hz
(b) 3.2 × 10⁷ Hz
(c) 3 × 10⁶ Hz
(d) 5 × 10⁷ Hz

Answer: B

Question. Consider a ray of light incident from air onto a slab of glass (refractive index n) of width d, at an angle q. The phase difference between the ray reflected bv the top surface of the glass and the bottom surface is 

Answer: A

Question. At the first minimum adjacent to the central maximum of a single-slit diffraction pattern, the phase difference between the Huygen's wavelet from the edge of the slit and the wavelet from the midpoint of the slit is :
(a) π/2 radian
(b) π radian 
(c) π/8 radian
(d) π/4 radian

Answer: B

Question. The wavefronts of a light wave travelling in vacuum are given by x + y + z = c. The angle made by the direction of propagation of light with the X-axis is
(a) 0º
(b) 45º
(c) 90º
(d) cos^–1(1/√3)

Answer: D

Question. The width of a slit is 0.012 mm. Monochromatic light is incident on it. The angular position of first bright line is 5.2º. The wavelength of incident light is
[sin 5.2º = 0.0906].
(a) 6040 Å
(b) 4026 Å
(c) 5890 Å
(d) 7248 Å

Answer: D

Question. In Fresnel’s biprism expt., a mica sheet of refractive index 1.5 and thickness 6 × 10^–6 m is placed in the path of one of interfering beams as a result of which the central fringe gets shifted through 5 fringe widths. The wavelength of light used is
(a) 6000 Å
(b) 8000 Å
(c) 4000 Å
(d) 2000 Å

Answer: A

Question. In young’s double-slit experiment, the intensity of light at a point on the screen where the path difference is λ is I, λ being the wavelength of light used. The intensity at a point where the path difference is λ/4 will be
(a) I/4
(b) I/2
(c) I
(d) zero

Answer: B

Question. In Young's double slit experiment, the fringes are displaced by a distance x when a glass plate of refractive index 1.5 is introduced in the path of one of the beams. When this plate is replaced by another plate of the same thickness, the shift of fringes is (3/2) x. The refractive index of the second plate is
(a) 1.75
(b) 1.50
(c) 1.25
(d) 1.00

Answer: A

Question. Light of wavelength 6.5 × 10^–7 m is made incident on two slits 1 mm apart. The distance between third dark fringe and fifth bright fringe on a screen distant 1 m from the slits will be
(a) 0.325 mm
(b) 0.65 mm
(c) 1.625 mm
(d) 3.25 mm

Answer: C

Question. Two nicols are oriented with their principal planes making an angle of 60º. Then the percentage of incident unpolarised light which passes through the system is
(a) 100
(b) 50
(c) 12.5
(d) 37.5

Answer: C

Question. When the light is incident at the polarizing angle on the transparent medium, then the completely polarized light is
(a) refracted light
(b) reflected light
(c) refracted and reflected light
(d) neither reflected nor refracted light

Answer: B

Question. The ratio of resQuestionolving powers of an optical microscope for two wavelengths λ₁ = 4000 Å and λ₂ = 6000 Å is 
(a) 9 : 4
(b) 3 : 2
(c) 16 : 81
(d) 8 : 27

Answer: B

Question. A beam of unpolarised light passes through a tourmaline crystal A and then through another such crystal B oriented so that the principal plane is parallel to A. The intensity of emergent light is I0. Now B is rotated by 45º about the ray.
The emergent light will have intensity
(a) I₀ / 2
(b) I₀ /√2
(c) I₀√2
(d) 2I₀

Answer: A

Question. In a double slit experiment, the two slits are 1 mm apart and the screen is placed 1 m away. A monochromatic light wavelength 500 nm is used. What will be the width of each slit for obtaining ten maxima of double slit within the central maxima of single slit pattern ? 
(a) 0.1 mm
(b) 0.5 mm
(c) 0.02 mm
(d) 0.2 mm

Answer: D

Question. A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct ?
(a) The angular width of the central maximum of the diffraction pattern will increase.
(b) The angular width of the central maximum will decrease.
(c) The angular width of the central maximum will be unaffected.
(d) Diffraction pattern is not observed on the screen in case of electrons.

Answer: B

 

THREE MARKS QUESTION

Question. Draw the type of wave front that corresponds to a beam of monochromatic light
(i) Coming from a very far off source and
(ii) Diverging radially from a point source
Answer : (i) Plane wave front (ii) Spherical wavefront

Question. Sketch the wave fronts corresponding to
(a) Converging rays
(b) Diverging rays
Answer : (i) wavefront is convex (ii) wavefront is concave

Question. In young’s double slit experiment, explain with reason in each case, how the interference pattern changes, when
(i) Separation between the slits is increased and
(ii) Screen is moved away from the plane of the slits.
Answer : . β = Dλ⁄d(i) Fringe width decreases as it is inversely proportional to the distance between the slits.
(ii) Fringe width is increased as it is directly proportional to the distance between slits and screen.

Question. How will the angular separation and visibility of fringes in Young’s double slit experiment change when
(i) Screen is moved away from the plane of the slits?
(ii) Wavelength of light is increased?
Answer : θ = λ⁄d (i) there will be no effect on angular fringe width.
(ii) Angular separation increases as it is directly proportional to the wavelength.

Question. In what way is diffraction from each slit is related to the interference pattern in a double slit experiment?
Answer : In Young’s double slit experiment there will be two diffraction pattern from two slits after superpose
it results into interference pattern.

Question. Define resolving power of a compound microscope. How does the resolving power of a compound microscope changes when –
(i) Refractive index of medium between the object and the objective lens increases.
(ii) Wavelength of radiation used is increased.
(iii) Decreasing the diameter of its objective.
Answer : Definition of resolving power. (i) R P increases (ii) RP decreases (iii) RP decreases

Question. How would the diffraction pattern of a single slit be affected when:
(i) The width of the slit is decreased
(ii) The monochromatic light is replaced with a light of higher frequency
(iii) The separation between the slit and screen is increased.
Answer : (i) Area of illumination increases
(ii) Fringe width is decreases
(iii) Fringe width increases

Question. (a) Using the phenomena of polarization, show how transverse nature of light can be demonstrated.
(b) Two polaroids P1 and P2 are placed with their axes perpendicular to each other. Unpolarised light of intensity I0 is incident on P1. A third Polaroid P3 is kept between P1 and P2 such that its axis makes an angle of 300 with that of P`1. Determine the intensity of light transmitted through P1 , P2 and P3.
Answer : When light is passed through a polarizer followed by an analyser, the intensity variation on the screen shows that light is transverse in nature.
Using the formula I = I0cos2Θ:
Θ1 = 300 angle between P1 and P3 and Θ2 = 600 angle between P3 and P2
The final intensity is 3I0/32

Question. (a) What is linearly polarized light? Describe briefly using a diagram how sunlight is polarized?
(b) Unpolarized light is incident on a Polaroid. How would the intensity of transmitted light change when the Polaroid is rotated?
Answer : (a) Definition of linearly polarized. Sunlight is polarized by scattering of light.
(b) there is no change in intensity of light.

Question. Two polaroids are placed at 900 to each other and transmitted intensity is zero. What happens when one more polaroid is placed between these two bisecting the angle between them. Take intensity of unpolarised light is I0.
Answer : Using the formula I = I0cos2Θ:
Θ1 = 450 angle between P1 and P3 and Θ2 = 450 angle between P3 and P2.
The final intensity is I0/4

Important Questions for NCERT Class 12 Physics Wave Optics

Question. Which one of the following phenomena is not explained by Huygen’s construction of wavefront ?
(a) Refraction
(b) Reflection
(c) Diffraction
(d) Origin of spectra

Answer : D

Question. The frequency of a light wave in a material is 2 × 10¹⁴ Hz and wavelength is 5000 Å. The refractive index of material will be
(a) 1.50
(b) 3.00
(c) 1.33
(d) 1.40

Answer : B

Question. In Young’s double slit experiment, we get 10 fringes in the field of view of monochromatic light of wavelength 4000Å. If we use monochromatic light of wavelength 5000Å, then the number of fringes obtained in the same field of view is 
(a) 8
(b) 10
(c) 40
(d) 50

Answer : A

Question. The Fraunhoffer ‘diffraction’ pattern of a single slit is formed in the focal plane of a lens of focal length 1 m. The width of slit is 0.3 mm. If third minimum is formed at a distance of 5 mm from central maximum, then wavelength of light will be 
(a) 5000 Å
(b) 2500 Å
(c) 7500 Å
(d) 8500 Å

Answer : A

Question. The refractive index of water is 1.33. What will be the speed of light in water?
(a) 4 × 10⁸ m/s
(b) 1.33 × 10⁸ m/s
(c) 3 × 10⁸ m/s
(d) 2.25 × 10⁸ m/s

Answer : D

Question. Light travels through a glass plate of thickness t and having a refractive index m. If c is the velocity of light in vacuum, the time taken by light to travel this thickness of glass is
(a) t/μc
(b) μt/c
(c) tmc
(d) tc/μ

Answer : B

Question. A star, which is emitting radiation at a wavelength of 5000 Å, is approaching the earth with a velocity of 1.5 × 10⁴ m/s. The change in wavelength of the radiation as received on the earth is
(a) 25 Å
(b) 100 Å
(c) zero
(d) 2.5 Å 

Answer : A

Question. Time taken by sunlight to pass through a window of thickness 4 mm whose refractive index is 3/2 is
(a) 2 × 10^–4 s
(b) 2 × 10⁸ s
(c) 2 × 10^–11 s
(d) 2 × 10¹¹ s 

Answer : C

Question. A beam of monochromatic light is refracted from vacuum into a medium of refractive index 1.5. The wavelength of refracted light will be
(a) depend on intensity of refracted light
(b) same
(c) smaller
(d) larger. 

Answer : C

Question. Green light of wavelength 5460 Å is incident on an air-glass interface. If the refractive index of glass is 1.5, the wavelength of light in glass would be (c = 3 × 10⁸ m s^–1)
(a) 3640 Å
(b) 5460 Å
(c) 4861 Å
(d) none of these.

Answer : A

Question. Ratio of intensities of two waves are given by 4 : 1. Then ratio of the amplitudes of the two waves is
(a) 2 : 1
(b) 1 : 2
(c) 4 : 1
(d) 1 : 4 

Answer : A

Question. Interference is possible in
(a) light waves only
(b) sound waves only
(c) both light and sound waves
(d) neither light nor sound waves

Answer : C

Question. In Young’s double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes
(a) double
(b) half
(c) four times
(d) one-fourth

Answer : C

Question. In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away, was found to be 0.2°. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water? (mwater = 4/3)
(a) 0.1°
(b) 0.266°
(c) 0.15°
(d) 0.05°

Answer : C

Question. In a Young’ double slit experiment if there is no initial phase difference between the light from the two slits, a point on the screen corresponding to the fifth minimum has path difference.
(a) 5.λ/2
(b) 10.λ/2
(c) 9.λ/2
(d) 11.λ/2

Answer : C

Question. In Young’s double slit experiment the separation d between the slits is 2 mm, the wavelength l of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same l and D) the separation between the slits needs to be changed to
(a) 1.8 mm
(b) 1.9 mm
(c) 2.1 mm
(d) 1.7 mm 

Answer : B

Question. Young’s double slit experiment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly
(a) 1.59
(b) 1.69
(c) 1.78
(d) 1.25

Answer : C

Question. The intensity at the maximum in a Young’s double slit experiment is I0. Distance between two slits is d = 5l, where l is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at a distance D = 10d ?
(a) 3/4 I₀
(b) I₀/2
(c) I₀
(d) I_0^/ 4

Answer : B

Question. Two slits in Young’s experiment have widths in the ratio 1 : 25. The ratio of intensity at the maxima and minima in the interference pattern, Imax /I min is
(a) 49/121
(b) 4/9
(c) 9/4
(d) 121/49

Answer : C

Question. A single slit Fraunhoffer diffraction pattern is formed with white light. For what wavelength of light the third secondary maximum in the diffraction pattern coincides with the second secondary maximum in the pattern for red light of wavelength 6500 Å? 
(a) 4400 Å
(b) 4100 Å
(c) 4642.8 Å
(d) 9100 Å

Answer : C

Question. At the first minimum adjacent to the central maximum of a single-slit diffraction pattern, the phase difference between the Huygen’s wavelet from the edge of the slit and the wavelet from the midpoint of the slit is
(a) π radian
(b) π /8 radian
(c) π/4 radian
(d) π/2 radian 

Answer: A

Question. A beam of light of l = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is
(a) 1.2 cm
(b) 1.2 mm
(c) 2.4 cm
(d) 2.4 mm 

Answer: D

Question. A parallel beam of fast moving electrons is incident normally on a narrow slit. A fluorescent screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statements is correct?
(a) The angular width of the central maximum will decrease.
(b) The angular width of the central maximum will be unaffected.
(c) Diffraction pattern is not observed on the screen in the case of electrons.
(d) The angular width of the central maximum of the diffraction pattern will increase.

Answer: A
 

Q1. The intensity of the light transmitted by a polaroid is half the intensity of the light incident on it. Give reason. 

Q2. Draw the shape of the refracted/reflected wave front when a plane wavefront incident on(i)prism (ii)convex mirror. 

Q3. Two objective lenses of aperture A1 and A2 (A1>A2) are used in two telescope. Write the ratio of their resolving power. 

Q4. For which angle of incidence a ray suffers minimum deviation of 30⁰ when incident on an equilateral prism. 

Q5. A convex lens and a concave lens of same focal length are kept in contact.find the focal length of the combination. 

Q6. On the basis of Huygens principle prove laws of reflection of light. 

Q7. In Youngs double slit experiment in I is the intensity emitted by each slit then prove that in interference pattern intensity varies between 0 and 4I. For which value of X first maxima will be obtained at P. 

Q8. If an object is placed at the bottom of a tank of depth d. Refractive index of water is μ.Find the area of the circle within which we can see the object from the surface of water. 

Q9. Focal length of double equi convex lens is twice of radius of curvature of its each face. Find the refractive index of lens. What would be the nature of lens if it is immersed in a liquid of refractive index 2. 

Q10. For concave spherical surface prove that n2/v – n1/u = (n2 – n1)/R. 

Q11. Derive the relation 1/f=1/v-1/u for a convex lens. Draw m vs v graph .Write how we can find focal length from this graph?

Please refer to the link below for CBSE Class 12 Physics Ray and Wave Optics Assignment.