Class 12 Physics Chapter 9 Ray Optics and Optical Instruments Solved Question Answers

(1) ar point of a myopic eye is 40 cm. The dioptic power of a corrective lens is:

[A] 40 D

[B] -4 D

[C] -2.5 D

[D] -0.25 diopter

Answer: -2.5 D

(2) A point object is placed at the centre of a glass sphere of radius 6 cm 3 and RI = 32. 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: 4 cm

(3) 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] π/2

[D] zero

Answer: zero

(4) The angle of deviation for a prism is greatest for:

[A] violet

[B] red

[C] orange

[D] yellow

Answer: violet

(5) A blue cross on the white background is illuminated with white light and is observed through red filter. What is seen?

[A] A red cross on a black background

[B] A blue cross on a red background

[C] A red cross on a blue background

[D] A black cross on a red background

Answer: A black cross on a red background

(6) For achromatic combination of lenses, if we use two lenses of focal length f’ and f₁ dipersive power to ω and ω’ respectively, then

[A] ω = ω₀, ω’= 2ω₀, f’ = 2f

[B] ω = ω₀, ω’ = 2ω₀, f’ = -2f

[C] ω = ω₀, ω’ = 2ω₀, f’ = f/2

[D] ω = ω₀, ω’ = 2ω₀, f’ = -f/2

Answer: ω = ω₀, ω’ = 2ω₀, f’ = -f/2

(7) The magnifying power of an astronomical telescope in normal adjustment is 100. The distance between the objective and the eyepiece is 101 cm. The focal length of the objectives and eyepiece is

[A] 10 cm and 1 cm respectively

[B] 100 cm and 1 cm respectively

[C] 1 cm and 100 cm respectively

[D] 1 cm and 10 cm respectively

Answer: 100 cm and 1 cm respectively

(8) An equiconvex lens of focal length f and power P is cut into two halves in thickness. The focal length and power of each half is

[A] f/2

[B] 2f

[C] f

[D] zero

Answer: 2f

(9) The power of a thin convex lens of glass is 5 D. When it is immersed in a liquid, then it behaves like a divergent lens of focal length 100 cm. The refractive index of the liquid is:

(Given, refractive index of glass = μ = 1.5)

[A] 3/5

[B] 1/2

[C] 2/3

[D] 5/3

Answer: 5/3

(10) A convex lens of focal length f = 20 cm is combined with a diverging lens of power 65 D. The power and the focal length of the combination is

[A] ‒1.5 D, 66.7 cm

[B] 1.5 D, 33.7 cm

[C] 5 D, 66.7 cm

[D] 5 D, 33.6 cm

Answer: 5 D, 66.7 cm

(11) What is the correct relation between the refractive indices n, n₁ and n₂ if the behavior of light rays is as shown in the figure given below?

[A] n₁

[B] n₁>n

[C] n₁ = n

[D] None of these

Answer: n₁

(12) The radius of curvature of a double concave lens is 20 cm. If the refractive index of glass with respect to air is 5/3 then, the focal length of this lens is

[A] 5 cm

[B] 15 cm

[C] ‒ 15 cm

[D] 20 cm

Answer: 15 cm

(13) Refractive index of material of a prism is √2. The angle of prism is 60o. What is the angle of minimum deviation?

[A] 30°

[B] 45°

[C] 60°

[D] 90°

Answer: 30°

(14) Rainbow is formed due to the combination of

[A] refraction and absorption

[B] dispersion and focusing

[C] dispersion and total internal reflection

[D] refraction and scattering

Answer: dispersion and total internal reflection

(15) If the critical angle for total internal reflection from a medium to vacuum is 30o, the velocity of light in the medium is

[A] 3 X 10⁸ m/s

[B] 1.5 X 10⁸ m/s

[C] 0.5 X 10⁸ m/s

[D] 0.2 X 10⁸ m/s

Answer: 1.5 X 10⁸ m/s

(16) In the figure given below there are two convex lenses L_A and L_B having focal lengths F_A and F_B respectively. The distance between L_A and L_B is

[A] F_A

[B] F_B

[C] F_A + F_B

[D] F_A ‒ F_B

Answer: F_A + F_B

(17) If an equiconvex lens of focal length f and power P is cut into half in thickness, what is the focal length and power of each half?

[A] Zero

[B] f/2

[C] f

[D] 2f

Answer: 2f

(18) The magnifying power of an astronomical telescope in normal adjustment is 100. What is the focal length of the objectives and eyepiece of the distance between them is 101 cm?

[A] 1 cm and 10 cm respectively

[B] 1 cm and 100 cm respectively

[C] 10 cm and 1 cm respectively

[D] 100 cm and 1 cm respectively

Answer: 100 cm and 1 cm respectively

(19) When a thin convex lens of glass 5D is immersed in a liquid, it behaves as a divergent lens of focal length 100 cm. What is the refractive index of the liquid?

[A] 1/2

[B] 2/3

[C] 3/5

[D] 5/3

Answer: 5/3

(20) A diverging lens of power 65 D is combined with a convex lens of focal length, f = 20 cm. What are the power and focal length of the combination?

[A] 5 D, 33.7 cm

[B] 5 D, 66.7 cm

[C] 1.5 D, 33.7 cm

[D] -1.5 D, 66.7 cm

Answer: 5 D, 66.7 cm

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NCERT Solutions for class 12 Physics | Chapter 9 - Ray Optics and Optical Instruments

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