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Class 12 Physics MCQ Questions of Ray Optics and Optical Instruments with Answers?

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Practice MCQ Question for Class 12 Physics chapter-wise

1. ​​​​​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

2. Which of the following cannot be polarised?

(a) radiowaves
(b) transverse waves
(c) sound waves
(d) X-rays

3. A convergent lens will become less convergent in :

(a) oil
(b) water
(c) both of (a) and (b)
(d) none of these

4. When light travels from one medium to another, which of the following does not change?

(a) frequency
(b) refractive index
(c) velocity
(d) wavelength

5. The air bubble inside water shine due to:

(a) Reflection
(b) Refraction
(c) T.l.R
(d) None of these

6. 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

7. The angle of deviation for a prism is greatest for:

(a) violet
(b) red
(c) orange
(d) yellow

8. In image formation from spherical mirrors, only paraxial rays are considered because they

(a) are easy to handle geometrically
(b) contain most of the intensity of the incident light
(c) form nearly a point image of a point source
(d) show minimum dispersion effect

9. When the angle of incidence of a light ray is greater than the critical angle it gets

(a) critically refracted
(b) totally reflected
(c) total internally reflected
(d) totally refracted

10. Critical angle of light passing from glass to water is minimum for

(a) red colour
(b) green colour
(c) yellow colour
(d) violet colour

11. Electromagnetic radiation belonging to................. region of spectrum is called light.

(a) 100 nm to 400 nm
(b) 400 nm to 750 nm
(c) 750 nm to 10 nm
(d) 1000 nm to 1400 nm

12. The turning back of light into the same medium after incident on a boundary separating two media is called

(a) reflection of light 
(b) refraction of light
(c) dispersion of light 
(d) interference of light

13. A person is six feet tall. How tall must a plane mirror be if he is able to see his entire length?

(a) 3 ft 
(b) 4.5 ft 
(c) 7.5 ft 
(d) 6 ft

14. When light is refracted, which of the following does not change?

(a) Wavelength 
(b) Frequency
(c) Velocity 
(d) Amplitude

15. The apparent flattening of the sun at sunset and sunrise is due to

(a) refraction
(b) diffraction
(c) total internal reflection
(d) interference

16. The rays of different colours fail to converge at a point after going through a converging lens. This defect is called

(a) spherical aberration
(b) distortion
(c) coma
(d) chromatic aberration

17. Chromatic aberration in a lens is caused by

(a) reflection 
(b) interference
(c) diffraction 
(d) dispersion

18. An astronomical telescope has a large aperture to

(a) reduce spherical aberration
(b) have high resolution
(c) increases span of observation
(d) have low dispersion

19. If a glass prism is dipped in water, its dispersive power

(a) increases
(b) decreases
(c) does not change
(d) may increase or decrease depending on whether the angle of the prism is less than or greater than 60º

20. In primary rainbow what is the order of colours observed from earth?

(a) Violet innermost, red outermost
(b) Red innermost, violet outermost
(c) Random
(d) White and dark alternatively

21. Astigmatism is corrected using

(a) cylindrical lens
(b) plano-convex lens
(c) plano- concave lens
(d) convex lens

22. Two thin lenses are in contact and the focal length of the combination is 80 cm. If the focal length of one lens is 20 cm, then the power of the other lens will be

(a) 1.66 D
(b) 4.00 D
(c) – 100 D
(d) – 3.75 D

23.  To an astronaut in a spaceship, the sky appears:

(a) Black
(b) White
(c) Green
(d) Blue

24. In total internal reflection when the angle of incidence is equal to the critical angle for the pair of media in contact, what will be angle of refraction?

(a) \(90^\circ\)
(b) \(180^\circ\)
(c) \(0^\circ\)
(d) equal to angle of incidence

25. Assertion: For observing traffic at our back, we prefer to use a convex mirror.

Reason: A convex mirror has a much larger field of view than a plane mirror or a concave mirror.

(a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion
(b) If both the assertion and reason are true but the reason is not a correct explanation of the assertion
(c) If the assertion is true but the reason is false
(d) If both the assertion and reason are false

Answer 2

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

Explanation: Light waves do not require a material medium for their propagation. Also they travel through vacuum. A metallic plate kept in the path of light rays gets heated up, showing that light involves transportation of energy.  Also speed of light is 3 \(\times\) 10⁸m/s which is constant.

2. Answer : (c) sound waves

Explanation: Sound waves are longitudinal and so they cannot be polarised.

3. Answer : (b) water

Explanation: Refractive index of oil and water both are greater than the refractive index of lens in air. Hence, the lens which was convex (focal length positive) in air will behave as a concave lens in that liquid. Hence, convex lens becomes less converging in both oil and water.

4. Answer : (a) frequency

Explanation: The property of light that does not change when it travels from one medium to another is frequency. The other properties of light like wavelength, speed of light changes when light travels from one medium to another.

5. Answer : (c) T.l.R

Explanation: The air bubble shines since the speed of light is faster inside the air bubble than in the water and therefore the light gets reflected away from the bubble around just like the mirror.

6. Answer : (c) of shorter λ

Explanation: For maximum accuracy in finding the position of an object using a light beam is achieved, when the light beam used is of shorter wavelength, because if the wavelength is longer, the spread in the wave will be more.

7. Answer : (a) violet

Explanation: Since the wavelength of violet light is the smallest, therefore maximum deviation will occur for violet light.

8. Answer : (c) 

Explanation: The reflected rays from a point source in a spherical mirror do not meet at a single point. To avoid it, rays close to the principal axis (Paraxial rays) are taken. It forms nearly a point image of a point source.

9. Answer : (c) total internally reflected

Explanation: When the angle of incidence is greater than the critical angle none of it is refracted, the ray is totally internally reflected, and the law of reflection is obeyed, i = r.

10. Answer : (d) violet colour

Explanation: The critical angle of light passing from glass to water is minimum for violet colour. The critical angle is very low for violet colour because of the refractive index of violet colour is very high.

11. Answer : (b) 400 nm to 750 nm

Explanation: Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma rays. Sunlight is also a form of EM energy, but visible light is only a small portion of the EM spectrum, which contains a broad range of electromagnetic wavelengths.

12. Answer : (a) reflection of light 

Explanation: Reflection is the abrupt change in the direction of propagation of a wave that strikes the boundary between two different media.

13. Answer : (a) 3 ft 

Explanation: To see his full image in a plane mirror a person requires a mirror of at least half of his height. 

14. Answer : (b) Frequency

Explanation: When a ray of light passes from one medium to the other medium, the physical quantities related with this ray of light such as velocity, wavelength, amplitude, etc changes such that the frequency of the wave always remains the same. Therefore, the frequency of the light does not change on its refraction.

15. Answer : (a) refraction

Explanation: Apparent flattening of the sun's disc at sunrise and sunset is due to atmospheric refraction. The density and the refractive index of the atmosphere decreases with altitude, so the rays above and below the sun on the horizon are refracted by different degrees.

16. Answer : (d) chromatic aberration

Explanation: This defect is known as chromatic aberration. It occurs because the lenses have different refractive indices for different wave lengths of light. Chromatic abberation itself manifests as "fringes" of colour along boundaries that seperate dark and bright parts of the image, because each colour in the optical spectrum can not be focused at a single common point.

17. Answer : (d) dispersion 

Explanation: Chromatic aberration is caused by the dispersion of light best demonstrated by using a prism (in our case, a lens). Dispersion is the separation of visible light into its different wavelengths.

18. Answer : (b) have high resolution

Explanation: The aperture of the objective lens is greater than the eye piece such that it can receive more light from the distant object and form a bright image of the object. Therefore, we can say that an astronomical telescope has a large aperture to have high resolution of a distant object. 

19. Answer : (b) decreases

Explanation: The dispersion decreases. When light enters from air to glass already disperses slightly and when this light enters to a glass prism the dispersion will be less as compared to the dispersion in air and glass prism.

20. Answer : (a) Violet innermost, red outermost

Explanation: In a primary rainbow red colour is on outermost arc, violet is in innermost arc. The red rays appear to be coming from a water droplet which subtends 42^∘ to the eyes whereas violet rays appear to be coming from a water droplet which subtends 40^∘ to the eyes.

21. Answer : (a) cylindrical lens

Explanation: The eye defect, astigmatism can be corrected by using a spherical cylindrical lens. Astigmatism can change the way to pass light and thus causes blurry and distorted vision.

22. Answer : (d) – 3.75 D

Explanation: P₂ = P− P₁ =\(\frac{100}{80}-\frac{100}{20}\) = −3.75D

23. Answer : (a) Black

Explanation: To an astronaut it will appear as black. On earth we see the blue sky due to presence of atmosphere. Atmosphere refracts light ray coming from the sun and we see the colour of sky. In space, due to the absence of the atmosphere the light rays do not refract and reach the astronomer's eyes therefore it appears black.

24. Answer : (a) \(90^\circ\)

Explanation: At i = i_c, refracted ray grazes with the surface.

So angle of refraction is 90^∘

25. Answer : (a) If both the assertion and the reason are true and the reason is a correct explanation of the assertion

Explanation: A convex mirror bends light as it reflects the light, and the farther away a point is from the center, the more the light is bent. As a result, an image formed in a convex mirror is smaller than an image in a plane (flat) mirror. Because the image is smaller, more images can fit onto the mirror, so a convex mirror provides for a larger field of view than a plane mirror. They are used whenever a mirror with a large field of view is needed to observe traffic.

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