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## Thursday, 28 January 2021

### CBSE Class 12 Physics - MCQ and Online Tests - Unit 9 - Ray Optics and Optical Instruments

#### CBSE Class 12 Physics – MCQ and Online Tests – Unit 9 – Ray Optics and Optical Instruments

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 9 – Ray Optics and Optical Instruments

Question 1.
The refractive indices (R.I.) of glass and water with respect to air are 3/2 and 4/3 respectively. The R.I. of glass w.r. to w ater is:
(a) 8/9
(b) 9/8
(c) 7/6
(d) 2

Question 2.
A thin glass (RI = $$\frac{3}{2}$$) lens has optical power of – 5D in air. Its optical power in a liquid medium with RI = 1.6 will be:
(a) -2.5 D
(b) 25 D
(c) -ID
(d) 0.625 D

Question 3.
A beam of light is incident at 60° to a plane surface. The reflected and refracted rays are perpendicular to each other. What is the R.I. of the surface:
(a) $$\frac{1}{√3}$$
(b) √3
(c) $$\frac{1}{3}$$
(d) 3

Question 4.
A concave mirror of focal length f produces an image n times the size of the object. If the image is real then the distance of the object is:
(a) (n – 1) f
(b) (n + 1) f
(c) ($$\frac{n+1}{n}$$)f
(d) ($$\frac{n-1}{n}$$)f

Answer: (c) ($$\frac{n+1}{n}$$)f

Question 5.
The phase difference between the electric and the magnetic field vectors in electromagnetic waves is
(a) $$\frac{π}{4}$$
(b) $$\frac{π}{2}$$
(c) π
(d) zero

Question 6.
A ray of light travelling in air is incident of a glass slab. The ray gets partly reflected and partly refracted. The phase difference between the reflected and the refracted waves is :
(a) $$\frac{π}{2}$$
(b) $$\frac{π}{4}$$
(c) π
(d) zero

Question 7.
A convergent lens will become less convergent in :
(a) oil
(b) water
(c) both of (a) and (b)
(d) none of these

Question 8.
Refractive index of water and glass are $$\frac{4}{3}$$ and $$\frac{5}{3}$$. A light ray is going to water from glass. Then, its critical angle will be:
(a) sin-1$$\frac{4}{5}$$
(b) sin-1$$\frac{5}{6}$$
(c) sin-1$$\frac{1}{2}$$
(d) sin-1($$\frac{2}{1}$$)

Answer: (b) sin-1$$\frac{5}{6}$$

Question 9.
On reflection from a denser medium, a light wave suffers a phase difference of:
(a) π
(b) $$\frac{π}{2}$$
(c) $$\frac{π}{4}$$
(d) 2π

Question 10.
Which of-the following is not a property of light?
(a) It can travel through vacuum
(b) It has a finite speed
(c) It requires a material medium for its propagation
(d) It involve transportation energy

Answer: (c) It requires a material medium for its propagation

Question 11.
Two points P and q are situated at the same distance from a source of light but on opposite sides. The plane difference between the light waves passing through P and q will be:
(a) n
(b) 2n
(c) $$\frac{π}{2}$$
(d) zero

Question 12.
The air bubble inside water shine due to:
(a) Reflection
(b) Refraction
(c) T.l.R.
(d) None of these

Question 13.
The branch of optics dealing with the formation of images using the concept of straight line propagation of light is called:
(a) geometrical optics
(b) physical optics
(c) corpuscular optics
(d) quantum optics

Question 14.
The angle of minimum deviation for an equilateral glass prism is 30°. Refractive index of the prism is:
(a) $$\frac{1}{√3}$$
(b) √2
(c) 1
(d) can’t be determined

Question 15.
When light travels from one medium to another, which of the following does not change?
(a) frequency
(b) refractive index
(c) velocity
(d) wavelength

Question 16.
Which of the following cannot be polarised?
(b) transverse waves
(c) sound waves
(d) X-rays

Question 17.
Two lens of power -15 D and +5 D are placed in contact co-axially. The focal length of equivalent lens is:
(a) -10 cm
(b) -20 cm
(c) +10 cm
(d) None

Question 18.
When a ray of light (white) enters a lens, undergoes a change is:
(a) wavelength
(b) velocity
(c) frequency
(d) both velocity and wavelength

Answer: (d) both velocity and wavelength

Question 19.
Radio waves from an antenna travel with the velocity of:
(a) light
(b) sound
(c) ultrasonics
(d) supersonics

Question 20.
Which produces additional luminiscence in a fluorescent tube?
(a) infra red rays
(b) ultraviolet rays
(c) micro waves

Question 21.
A point object is placed at the centre of a glass sphere of radius 6 cm 3 and RI = $$\frac{3}{2}$$. The distance of virtual image from the surface of the sphere is :
(a) 2 cm
(b) 4 cm
(c) 6 cm
(d) 12 cm

Question 22.
When a beam of light is used to determine the position of an object, the maximum accuracy is achieved if the light is :
(a) polarized
(b) of longer λ
(c) of shorter λ
(d) of high intensity

Question 23.
A convex lens is dipped in a liquid, whose R.I. is equal to that of R.I. of material of the lens. Then its focal length will:
(a) become zero
(b) become infinite
(c) reduce
(d) increase

Question 24.
The RI. of the material of a prism is √2 and its refracting angle is 30°. One of the refracting surface of the prism is made a mirror. A beam of monochromatic light entering the prism from the other face retraces its path, after reflection from mirror surface. The angle of incidence on prism is:
(a) 0°
(b) 30°
(c) 45°
(d) 60°

Question 25.
The velocity of light in vacuum is 3 × 1010 cms-1. The velocity of light in a medium (µ = 1.5) is:
(a) 2 × 1010cms-1
(b) 4.5 × 1010cms-1
(c) 1.5 × 1010cms-1
(d) None of these

Question 26.
Light year is the unit of:
(a) distance
(b) time
(c) intensity of light
(d) None of these

Question 27.
If a mirror is approaching you at a speed of 10 ms^1, the speed with which your image approach you is:
(a) 10 ms-1
(b) 5 ms-1
(c) 20 ms-1
(d) 15 ms-1

Question 28.
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 two objects, which can be resolved by the telescope, when seen in the light of mean λ = 5000 A is of the order of:
(a) 5 mm
(b) 5 cm
(c) 0.5 m
(d) 5 m

Question 29.
Which of the following is not essential for the formation of a pure spectrum?
(a) parallel beam of light
(b) narrow beam of light
(c) screen
(d) prism in the minimum deviation position

Question 30.
A certain far-sighted person cannot see objects closer to the eye than 100 cm. The power of the lens which will enable him to read at a distance of 25 cm will be?
(a) 3D
(b) 1D
(c) 4D
(d) 2D