Railway Science (Physics-Light and Optics) (Part-VIII)

Total Questions: 12

1. A concave mirror produces 3 times magnified real image of an object placed at 5 cm in front of it. At what distance from the front of the mirror is the image located? [RRB JE 23/05/2019 (Afternoon)]

Correct Answer: (c) 15 cm
Solution:

2. A concave lens has a focal length 15 cm. If the object is placed at 30 cm from the lens, what is the image distance? [RRB JE 24/05/2019 (Afternoon)]

Correct Answer: (b) -10 cm
Solution:

3. If the radius of curvature of a concave mirror is 6.2 cm, its focal length is __________ cm. [RRB Group D 18/09/2018 (Afternoon)]

Correct Answer: (b) 3.1
Solution:

Given, R = 6.2 cm.
āˆµ Focal length, f = R/2 where, š‘…Ā  is the radius of curvature.
āˆ“ f = 6.2/2 = 3.1 cm.

4. If an object is placed 10 cm away from a convex mirror of radius of curvature 5 cm, what will be its magnification? [RRB Group D 18/09/2018 (Evening)]

Correct Answer: (b) 0.2
Solution:

5. The speed of light in a medium of refractive index 1.5 is __________ . [RRB Group D 20/09/2018 (Evening)]

Correct Answer: (d) 2.0 Ɨ 10āø m / s
Solution:

Refractive Index (n)

6. The focal length of a concave mirror with a radius of curvature of 20.0 cm is: [RRB ALP Tier - I (09/08/2018) Afternoon]

Correct Answer: (c) 10cm
Solution:

The radius of curvature is twice the focal length. In other words, focal length is half of the radius of curvature.
Focal length
(f) = š‘…š‘Žš‘‘š‘–š‘¢š‘  š‘œš‘“ š‘š‘¢š‘Ÿš‘£š‘Žš‘”š‘¢š‘Ÿe (R)/2 .
Given that R = 20 cm so, f = 20/2 = 10 cm.

7. An incident ray strikes a plane mirror at an angle of 20Ā° with the mirror. The angle between the incident ray and reflected ray is _______. [RRB ALP Tier - I (13/08/2018) Afternoon]

Correct Answer: (c) 140Ā°
Solution:

The incident ray, reflected ray and normal ray to the mirror, all lie on the same plane. The angle of incidence and angle of reflection are equal. An incident ray strikes a plane mirror at an angle of 20Ā° with the mirror. Therefore, it will make an angle (90Ā° - 20Ā° = 70Ā° with the normal. Angle of incidence = Angle of reflection = 70Ā° Therefore, the angle between the incident ray and the reflected ray = 70Ā°+ 70Ā° = 140Ā°

8. A lens has a power + 2.0D. The type of lens and its focal length will be______. [RRB ALP Tier - I (14/08/2018) Evening]

Correct Answer: (c) convex, 0.5 m
Solution:

Given, lens of power P = (2.0) D.
Power (P) = 1/f , f = 1/pĀ  = 1/2,
F = 0.5 m. (focal length is positive, it is a convex lens)
The SI unit of power of a lens is dioptre (D).

9. An object is placed at a distance of 20 cm from a convex lens of focal length 10 cm. The image is formed at a distance of: [RRB ALP Tier - I (29/08/2018) Morning]

Correct Answer: (b) 20 cm
Solution:

10. A convex lens has a focal length of 50 cm. Calculate its power. [RRB ALP Tier - I (29/08/2018) Afternoon]

Correct Answer: (c) 2 D
Solution: