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## Thursday, 28 January 2021

### CBSE Class 12 Physics - MCQ and Online Tests - Unit 10 - Wave Optics

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 10 – Wave Optics

Every year CBSE conducts board exams for 12th standard. These exams are very competitive to all the students. So our website provides online tests for all the 12th subjects. These tests are also very effective and useful for those who preparing for competitive exams like NEET, JEE, CA etc. It can boost their preparation level and confidence level by attempting these chapter wise online tests.

These online tests are based on latest CBSE Class 12 syllabus. While attempting these our students can identify the weak lessons and continuously practice those lessons for attaining high marks. It also helps to revise the NCERT textbooks thoroughly.

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 10 – Wave Optics

Question 1.
For sustained interference, we need two sources which
(a) of the same intensity
(b) of the same amplitude
(c) having a constant phase difference
(d) None of these

Answer: (c) having a constant phase difference

Question 2.
When a polaroid is rotated, the intensity of light does not vary. The incident light may be:
(a) unpolarised
(b) completely polarised
(c) partially plane polarised
(d) None of the above

Question 3.
Two sources of light are said to be coherent when both give out light waves of the same:
(a) amplitude and phase
(b) intensity and wavelength
(c) speed
(d) wavelength and a constant phase difference

Answer: (d) wavelength and a constant phase difference

Question 4.
When a polaroid is rotated, the intensity of light varies but never reduces to zero. It shows that the incident light is:
(a) unpolarised
(b) completely plane polarised
(c) partially plane polarised
(d) None of the above

Question 5.
The intensity of light emerging from the two slits, in Young’s experiment is in the ratio 1 : 4. The ratio of,the intensity of the minimum to that of the consecutive maximum will be:
(a) 1 : 4
(b) 1 : 9
(c) 1 : 16
(d) 2 : 3

Question 6.
What happens if one of the slits, say S1 in Young’s double , slit experiment-is covered with a glass plate which absorbs half the intensity of light from it?
(a) The bright fringes become less-bright and the dark fringes have a finite light intensity
(b) The bright fringes become brighter and the dark fringes become darker
(c) The fringe width decreases
(d) No fringes will be observed

Answer: (a) The bright fringes become less-bright and the dark fringes have a finite light intensity

Question 7.
Poisson’s bright spot was discovered by:
(a) Fresnel
(b) Rayleigh
(c) Poisson
(d) Fraunhoffer

Question 8.
(a) The two sources do not emit light of the same wavelength
(b) The two sources emit waves which travel with different speeds
(c) The two sources emit light waves of different amplitudes
(d) There is not constant phase difference between the waves emitted by the two sources

Answer: (d) There is not constant phase difference between the waves emitted by the two sources

Question 9.
The theory of expanding universe is confirmed by the observation of the spectral lines of the star, which shows :
(a) green shift
(b) red shift
(c) violet shift
(d) yellow shift

Question 10.
What happens to the interference pattern the two slits S1 and S2 in Young’s double experiment are illuminated by two independent but identical sources?
(a) The intensity of the bright fringes doubled
(b) The intensity of the bright fringes becomes four times
(c) Two sets of interference fringes overlap
(d) No interference pattern is observed

Answer: (d) No interference pattern is observed

Question 11.
The application of Doppler effect are:
(a) Doppler spectrometer
(c) Doppler velocimeter
(d) All of these

Question 12.
A single slit diffraction pattern is obtained using a beam of red light What happened the red light is replaced by the blue light?
(a) There is no change in diffraction pattern
(b) Diffraction fringes become narrower and crowded
(d) Diffraction fringes become broader and farther apart
(d) The diffraction pattern disappear

Answer: (b) Diffraction fringes become narrower and crowded

Question 13.
Which of the following is conserved when light waves interefere?
(a) phase
(b) intensity
(c) amplitude
(d) none of these

Question 14.
The angle of minimum deviation of a prism depends upon the aggie of:
(a) incidence
(b) reflection
(c) prism
(d) none of these

Question 15.
Out of the following Statements which is not correct?
(a) When unpolarised light passes through Nicol’s prism, the emergent light is elliptically polarized
(b) Nicol’s prism works on the principle of double refraction and T.l.R.
(c) Nicol’s prism can be used both the produce and analyse polarized light
(d) Calcite and Quartz are both double refracting crystal

Answer: (a) When unpolarised light passes through Nicol’s prism, the emergent light is elliptically polarized

Question 16.
In Young’s double slit experiment, a maximum is obtained when the path difference between the interfering waves is (n ∈ l):
(a) nλ
(b) n $$\frac{λ}{2}$$
(c) (2n + 1) $$\frac{λ}{2}$$
(d) (2n – 1) $$\frac{λ}{4}$$

Question 17.
In vacuum, the speed of light depends upon :
(a) frequency
(b) velocity
(c) wave length
(d) None of these

Question 18.
Polaroid glasses is used in sun glasses because :
(a) It reduces the light intensity to half on account of polarization
(b) It is fashionable
(c) It has good colour
(d) It is cheaper

Answer: (a) It reduces the light intensity to half on account of polarization

Question 19.
In Young double slit experiment, a minimum is obtained when the phase difference of the superposing waves, is (n ∈ l):
(a) nπ
(b) (n + $$\frac{1}{2}$$)π
(c) (2n + 1)π
(d) zero

Question 20.
The fringe width (β) of a diffraction pattern and the slit width d are related as:
(a) β ∝ d
(b) β ∝$$\frac{1}{d}$$
(c) β ∝ √d
(d) β ∝ $$\frac{1}{d^2}$$

Answer: (b) β ∝$$\frac{1}{d}$$

Question 21.
Between the slit is id\ the distance between the slit and the screen is α, with light of wavelength λ, the number of fringe observed per metre on the screen is:
(a) $$\frac{δy}{α}$$
(b) $$\frac{Dα}{λ}$$
(c) $$\frac{α}{Dλ}$$
(d) $$\frac{λd}{D}$$

Answer: (a) $$\frac{δy}{α}$$

Question 22.
A person cannot see object clearly beyond 50 cm. The pow er of the lens to correct his vision is :
(a) +0.5 dioptre
(b) -0.5 dioptre
(c) -2 dioptre
(d) +2 dioptre

Question 23.
The focal length of the lens is 50 cm; then its power is:
(a) +2D
(b) +1D
(c) -2D
(d) -1D

Question 24.
he minimum value of the refractive index is:
(a) zero
(b) 1
(c) less than 1 but not zero
(d) more than 1

Answer: (c) less than 1 but not zero

Question 25.
Polarization of light prove the :
(a) corpuscular nature of light
(b) quantum nature of light
(c) Transverse wave nature of light
(d) Longitudinal wave nature of light

Answer: (c) Transverse wave nature of light

Question 26.
A phase difference of 5π corresponds to a path difference (in terms of λ) of:
(a) 5λ
(b) 10λ.
(c) 5λ/2
(d) 2λ

Question 27.
A polaroid produces a strong beam of light which is :
(a) circularly polarised
(b) elliptically polarised
(c) plane polarised
(d) unpolarised

Question 28.
In Young’s double slit experiment the distance between the slit and the screen is doubled and the separation between the slit is reduced to half. The fringe width:
(a) is doubled
(b) become four time
(c) is halfed
(d) remain unchanged

Question 29.
In Young’s double slit experiment, the central point on the screen is:
(a) bright
(b) dark
(c) first bright and later dark
(d) first dark and later bright

Question 30.
Images of a distant lamp seen through a fire cloth rotate on rotating the cloth. This is due to the phenomenon of:
(a) interference
(b) diffraction
(c) polarisation
(d) scattering

Question 31.
In a Young’s double slit experiment the distance between the slit is 1 mm and the distance of screen from the slit is 1 m. If light of wavelength 6000 A is used then the fringe width is:
(a) 0.4 mm
(b) 0.5 mm
(c) 0.6 mm
(d) 0.8 mm

Question 32.
C.V. Raman was awarded the Nobel prize for his work associated with which of the following phenomenon of radiations?
(a) scattering
(b) diffraction
(c) interference
(d) polarisation

Question 33.
Light takes 10-10 to cross a glass slab. What is the thickness of the glass slab?
(a) 2 cm
(b) 3 cm
(c) 2.5 cm
(d) 3.5 cm

Question 34.
A young’s double slit experiment uses a monochromatic source. The shape of interference fringes formed on a screen is :
(a) parabola
(b) straight line
(c) circle
(d) hyperbola

Question 35.
A monochromatic light is refracted from air into a glass of refractive index µ. The ratio of the wavelengths of the incident and the refracted waves is:
(a) 1 : µ
(b) 1 : µ²
(c) µ : 1
(d) µ² : 1

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