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
Answer
Answer: (b) 9/8
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
Answer
Answer: (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
Answer
Answer: (b) √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
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
Answer
Answer: (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
Answer
Answer: (c) π
Question 7.
A convergent lens will become less convergent in :
(a) oil
(b) water
(c) both of (a) and (b)
(d) none of these
Answer
Answer: (b) water
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
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
Answer
Answer: (a) π
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
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
Answer
Answer: (d) zero
Question 12.
The air bubble inside water shine due to:
(a) Reflection
(b) Refraction
(c) T.l.R.
(d) None of these
Answer
Answer: (c) T.l.R.
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
Answer
Answer: (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
Answer
Answer: (b) √2
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
Answer
Answer: (a) frequency
Question 16.
Which of the following cannot be polarised?
(a) radiowaves
(b) transverse waves
(c) sound waves
(d) X-rays
Answer
Answer: (c) sound waves
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
Answer
Answer: (a) -10 cm
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
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
Answer
Answer: (a) light
Question 20.
Which produces additional luminiscence in a fluorescent tube?
(a) infra red rays
(b) ultraviolet rays
(c) micro waves
(d) radio waves
Answer
Answer: (b) ultraviolet rays
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
Answer
Answer: (b) 4 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
Answer
Answer: (c) of shorter λ
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
Answer
Answer: (b) become infinite
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°
Answer
Answer: (c) 45°
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
Answer
Answer: (a) 2 × 1010cms-1
Question 26.
Light year is the unit of:
(a) distance
(b) time
(c) intensity of light
(d) None of these
Answer
Answer: (a) distance
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
Answer
Answer: (c) 20 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
Answer
Answer: (a) 5 mm
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
Answer
Answer: (c) screen
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
Answer
Answer: (a) 3D
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