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

Total Questions: 50

11. When a ray of light travels from a denser medium to a rarer medium, it bends: [RRB ALP Tier - I (10/08/2018) Morning]

Correct Answer: (a) away from the normal and speeds up
Solution:Refraction - The bending of light rays after entering a medium where its speed is different. Natural Phenomenon: Bending of Object in a Glass, Shallower Swimming Pool, Atmospheric Refraction and Setting sun, Twinkling Star.

12. The velocity of light in vacuum is: [RRB ALP Tier - I (10/08/2018) Afternoon]

Correct Answer: (c) 3 × 10⁸ ms⁻¹
Solution:

(c) 3 × 10⁸ ms⁻¹  . Speed of light - The speed at which light propagates through the medium. The speed of light in free space has the same value in all inertial frames of reference. Speed of light (c) = f × λ , where f = frequency of light, λ = wavelength of light.

13. The centre of the reflecting surface of a spherical mirror is called the: [RRB ALP Tier - I (10/08/2018) Afternoon]

Correct Answer: (b) pole
Solution:

Pole. Aperture - The diameter of the reflecting surface of a spherical mirror. Focus (F) - The point at which the light rays concentrate or appear to concentrate after reflecting from the spherical mirror. Centre of Curvature (C) - The centre of curvature is the centre of the sphere of which the spherical mirror is a part. Radius of curvature (R) - Distance of center of curvature from pole.

14. Name the type of mirror used in the headlight of vehicles: [RRB ALP Tier - I (10/08/2018) Evening]

Correct Answer: (a) Concave mirror
Solution:

Concave Mirror (Converging mirror)- It is that mirror whose reflecting surface is toward the center of the curvature. Image formed - Real, virtual, erect or inverted. Uses - Shaving mirrors, Headlights and Solar furnaces.

15. Which of the following is a Non-Luminous body? [RRB ALP Tier - I (10/08/2018) Evening]

Correct Answer: (b) Moon
Solution:

Moon. Non-luminous objects are which can not emit light on their own. These objects reflect light from luminous bodies. Examples - Moon, Earth. Luminous objects are those objects which emit light on their own. Examples - Sun, flame of a burning candle, Firefly and Glowing bulb.

16. If the power of a corrective lens is +2.0D, then it is a: [RRB ALP Tier - I (13/08/2018) Morning]

Correct Answer: (c) convex lens
Solution:

Convex lenses (converging lenses) have positive power because their focal lengths (distance between the center of the lens to the focus) are positive; It converges the beam of light coming from outside and focus it to a point on the other side; It is thicker at the center and thinner at edges.

17. A curved mirror where the reflecting surface is curved inwards is called a: [RRB ALP Tier - I (13/08/2018) Morning]

Correct Answer: (b) concave mirror
Solution:

Concave mirror (converging mirrors) reflects and focuses incoming light rays (parallel) at a point called Focus point; Depending on the distance of an object from the reflecting surface, different types of images are formed. A plane mirror is a mirror with a flat (planar) reflective surface. Plano-convex lenses/Mirrors are positive focal length elements that have one spherical surface and one flat surface.

18. A lemon kept in water in a glass tumbler appears to be bigger than its actual size when viewed from the sides. This is because of: [RRB ALP Tier - I (14/08/2018) Morning]

Correct Answer: (b) refraction of light
Solution:

Refraction of light. As the light waves travel from water/glass medium (denser) to air medium (rarer), it bends away from the normal, hence projecting an image larger than the object.

19. If the angle of incidence formed on a concave mirror at a point is 30° then the angle of reflection will be: [RRB ALP Tier - I (17/08/2018) Afternoon]

Correct Answer: (b) 30
Solution:

30°. According to laws of reflection, for an incident ray and its corresponding reflected ray, the angle of incidence is always equal to the angle of reflection. Thus, if the angle of incidence is 30° then the angle of reflection will also be equal to 30°.

20. What is the Centre of Curvature of a spherical mirror? [RRB ALP Tier - I (17/08/2018) Evening]

Correct Answer: (b) It is the centre of a hollow sphere of which the spherical mirror is a part.
Solution:The distance between the Pole and the Principal Focus of the spherical mirror is termed as the focal length 'f' of the mirror. The Pole of a spherical mirror 'P' (convex or concave) is the center of the reflecting surface of the spherical mirror. It lies on the surface of the spherical mirror. Pole: The center of a spherical mirror.