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**Q.1. A ray is incident at an angle of incidence i on one surface of a small angle prism (with angle of prism A) and emerges normally from the opposite surface. If the refractive index of the material of the prism is m, then the angle of incidence is nearly equal to: (2020)A: μAB: μA/2C: A/2μD: 2A/μ**

1 sin i = μ. sin A

for small angle approximation

sin θ = θ

i = μA

A: 24 × 10

B: 48 × 10

C: 10 × 10

D: 12 × 10

= 400 w

∴ in 1 minute = 400 × 60

= 24000

A: When the light rays undergo two internal reflections in a water drop, a secondary rainbow is formed

B: The order of colours is reversed in the secondary rainbow

C: An observer can see a rainbow when his front is towards the sun

D: Rainbow is a combined effect of dispersion refraction and reflection of sunlight

Ans:

Solution:

Rainbow can't be observed when observer faces towards sun.

A: 2 : 1

B: 1 : 2

C: 2 : 3

D: 3 : 4

Ans:

Solution:

Equivalent focal length in air

When glycerin is filled inside, glycerin lens behaves like a diverging lens of focal length (-f)

**Q.5.**** 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? (2019)A: 180°B: 0°C: Equal to angle of incidenceD: 90°Ans: **D

Solution:

At i = i

So angle of refraction is 90°.

A: 60°

B: 45°

C: 30°

D: zero

Ans:

Solution:

**Q.7. ****An object is placed at a distance of 40 cm from a concave mirror of focal length 15 cm. If the object is displaced through a distance of 20 cm to wards the mirror, the displacement of the image will be:- (2018)A: 30 cm away from the mirrorB: 36 cm away from the mirrorC: 30 cm towards the mirrorD: 36 cm towards the mirrorAns:** B

Solution:

A: small focal length and large diameter

B: large focal length and small diameter

C: large focal length and large diameter

D: small focal length and small diameter

Ans: C

Solution:

For astronomical refracting telescope

Angular magnification is for large focal length

A: y/x

B: x/2y

C: x/y

D: y/2x

**Q.10. The ratio of resolving powers of an optical microscope for two wave lengths λ _{1} = 4000 Å and λ_{2} = 6000 Å is :- (2017)**B

A: 9 : 4

B: 3 : 2

C: 16 : 81

D: 8 : 27

Ans:

Solution:

**Q.11.** **A thin prism having refracting angle 10° is made of glass of refractive index 1.42. This prism is combined with another thin prism of glass of refractive index 1.7. This combination produces dispersion without deviation. The refracting angle of second prism should be :- (2017)A: 6°B: 8°C: 10°D: 4°Ans: **A

Solution:

(μ -1)A + (μ'-1)A = 0

(μ-1)A |(μ'-1)A'|

(1.42 -1)x10° = (1.7 -1)A'

4.2 = 0.7A'

A' = 6°

A: 54 cm

B: 37.3 cm

C: 46 cm

D: 50 cm

Ans: A

Solution:

According to a question,

Focal length of the objective lens, F

Focal length of eyepiece, F

Object distance for objective lens (u

Applying lens formula for objective lens,

Image will be formed at the focus of a eyepiece lens.

So, for normal adjustment distance between objectives and eyepiece (length of tube) will be, v + F

Column - 1 Column - 2

B: A → b and c; B → b and c; C → b and d; D → a and d

C: A → a and c; B → a and d; C → a and b; D → c and d

D: A → a and d; B → b and c; C → b and d; D → b and c

Ans:

Solution:

(A) m = -2, so image is magnified and inverted. Which is possible only for concave mirror. since image is i inverted so it will be real.

(B) M = -1/2 , so image is inverted and diminished. since image is inverted, so it will be real, and the mirror will be concave.

(C) M = +2, image is magnified so the mirror will be concave. Image is erect so it will be virtual.

(D) m = +1/2 , image is erect so image will be virtual. Image is virtual and diminished, so the mirror should be convex.

A: 30 deg; 1/√2

B: 45 deg; 1/√2

C: 30 deg; √2

D: 45 deg; √2

Ans:

**Q.15. ****The refracting angle of a prism is A, and refractive index of the material of the prism is cot (A/2). The angle of minimum deviation is : (2015)A: 180º + 2AB: 180º - 3AC: 180º - 2AD: 90º - AAns: **C

Solution:

**Q.16. ****Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of 20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled with oil of refractive index 1.7. The focal length of the combination is : (2015)A: 50 cmB: -20 cmC: -25 cmD: -50 cmAns: **D

Solution:

**Q.17. ****The angle of a prism is ‘A’. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2A on the first surface returns back through the same path after suffering reflection at the silvered surface. The refractive index μ, of the prism is : (2014)A: 1/2 cos AB: tan AC: 2 sin A**

Ans:

Solution:

**Q.18.**** If the focal length of objective lens is increased then magnifying power of : (2014)A: microscope and telescope both will decreaseB: microscope will decrease but that of telescope will increaseC: microscope will increase but that of telescope will decreaseD: microscope and telescope both will increaseAns: **B

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