CBSE Class 12 Physics Ray and Wave Optics Assignment Set B

Question. Two waves having the intensities in the ratio of 9 : 1 produce interference. The ratio of maximum to minimum intensity is
(a) 10 : 8
(b) 9 : 1
(c) 4 : 1
(d) 2 : 1

Answer: C

Question. Four independent waves are expressed as
(i) y₁ = a₁ sin~t (ii) y₂ = a₂ sin 2ωt
(iii) y₃ = a₃ cos^~t and (iv) y₄ = a₄ sin (ωt + π/3)
The interference is possible between
(a) (i) and (iii)
(b) (i) and (iv)
(c) (iii) and (iv)
(d) not possible at all

Answer: D

Question. Consider sunlight incident on a slit of width 10⁴ A. The image seen through the slit shall
(a) be a fine sharp slit white in colour at the center.
(b) a bright slit white at the center diffusing to zero intensities at the edges.
(c) a bright slit white at the center diffusing to regions of different colours.
(d) only be a diffused slit white in colour.

Answer: A

Question. In a Young’s double-slit experiment the fringe width is found to be 0.4 mm. If the whole apparatus is dipped in water of refractive index 4/3, without disturbing the arrangement, the new fringe width will be
(a) 0.30 mm
(b) 0.40 mm
(c) 0.53 mm
(d) 0.2 mm

Answer: A

Question. In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength m 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 λ 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. In a Young’s double slit experiment, the source is white light. One of the holes is covered by a red filter and another by a blue filter. In this case
(a) there shall be alternate interference patterns of red and blue.
(b) there shall be an interference pattern for red distinct from that for blue.
(c) there shall be no interference fringes.
(d) there shall be an interference pattern for red mixing with one for blue.

Answer: C

Question. In a Young’s double-slit experiment, the source S and two slits A and B are horizontal, with slit A above slit B. The fringes are observed on a vertical screen K. The optical path length from S to B is increased very slightly (by introducing a transparent material of higher refractive index) and optical path length from S to A is not changed. As a result, the fringe system on K moves
(a) vertically downwards slightly
(b) vertically upwards slightly
(c) horizontally slightly to the left
(d) horizontally slightly to the right

Answer: A

Question. In Young’s double-slit experiment, the distance between the slit sources and the screen is 1 m. If the distance between the slits is 2 mm and the wavelength of light used is 600 nm, the fringe width is
(a) 3 mm
(b) 0.3 mm
(c) 6 mm
(d) 0.6 mm

Answer: B

Question. The Young’s double-slit experiment is performed with blue and green lights of wavelengths 4360 Å and 5460 Å respectively. If x is the distance of 4th maxima from the central one, then
(a) (x)_blue = (x)_green
(b) (x)_blue > (x)_green
(c) (x)_blue < (x)_green
(d) (x)_blue / (x)_green = 5460 / 4360

Answer: C

Question. The angular resolution of a 10 cm diameter telescope at a-wavelength 500 nm is of the order of
(a) 10^–4 rad
(b) 10^–6 rad
(c) 10^–3 rad
(d) 10⁷ rad

Answer: B

Question. A telescope has an objective lens of 10 cm diameter and is situated at a distance of 1 km from two objects. The minimum distance between these objects that can be resolved by the telescope, when the mean wavelength of light is 5000 Å is of the order of
(a) 5 mm
(b) 5 cm
(c) 2.5 m
(d) 5 m

Answer: A

Question. Which of the following phenomenon cannot take place with longitudinal waves (e.g., sound waves)?
(a) reflection
(b) interference
(c) diffraction
(d) polarisation

Answer: D

Question. Unpolarised light is incident from air on a plane surface of a material of refractive index n. At a particular angle of incidence i, it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options is correct for this situation?
(a) Reflected light is polarised with its electric vector parallel to the plane of incidence
(b) Reflected light is polarised with its electric vector perpendicular to the plane of incidence
(c) i = sin^–1 (1/n)
(d) i = tan^–1 (1/n)

Answer: A

Question. An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
(a) small focal length and large diameter
(b) large focal length and small diameter
(c) large focal length and large diameter
(d) small focal length and small diameter

Answer: B

Question. A ray of light is incident on the surface of a glass plate at an angle of incidence equal to Brewsters angle φ. If n represents the refractive index of glass with respect to air, then the angle between the reflected and refracted rays is
(a) 90 + φ
(b) sin^–1 (n cosΦ)
(c) 90°
(d) 90° - sin 1(sin Φ / n)

Answer: B

Question. Consider the diffraction pattern for a small pinhole. As the size of the hole is increased
(a) the size decreases
(b) the intensity increases
(c) the size increases
(d) the intensity decreases

Answer: A, B

Question. For light diverging from a point source
(a) the wavefront is spherical.
(b) the intensity decreases in proportion to the distance squared.
(c) the wavefront is parabolic.
(d) the intensity at the wavefront does not depend on the distance.

Answer: A, B

Fill in the Blanks

Question. A beam of light is incident normally upon a polariser and the intensity of emergent beam is IO.
The intensity of the emergent beam is found to be unchanged when the polariser is rotated about an axis perpendicular to the pass axis. Incident beam is _________________ in nature.
Answer: unpolarised

Question. The value of Brewster angle depends on the nature of the transparent refracting medium and the _________________ of light used.
Answer: wavelength

Question. In Young’s double slit experiment, the fringe width is given by _________________.
Answer: b = Dλ/d

Question. The phase difference between two waves in _________________ interference is given as an even multiple of p.
Answer: constructive

Question. Fringe width is different as separation between two consecutive _________________ or _________________.
Answer: maxima, minima

Question. _________________ of light occurs when size of the obstacle of aperture is comparable to the wavelength of light.
Answer: Diffraction

Question. Continuous locus of oscillation with constant phase is called as _________________.
Answer: wave-front

Question. In interference and _________________, the light energy is redistributed, increases in one region and decreases in other.
Answer: diffraction

Question. At polarising angle the refracted and reflected rays are _________________ to each other.
Answer: perpendicular

Question. The tangent of angle of polarization as light ray travels from air to glass is equal to the refractive index. This law is called as _________________.
Answer: Brewster’s law