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

Total Questions: 50

1. In a Concave mirror, where should the Object be placed to get a real, inverted and diminished image between C and F ? [RRB Group D 31/10/2018 (Afternoon)]

Correct Answer: (c) Beyond C
Solution:

Beyond C. Image formation by concave mirror for different positions of the object: Position of the object (position, size of the image): At infinity (At focus, highly diminished and point sized), At C ( At C, same size), Between C and F (beyond C, enlarged), At F (At infinity, highly enlarged), Between P and F (behind the mirror, enlarged).

2. ________ color has the smallest angle of deviation. [RRB Group D 1/11/2018 (Afternoon)]

Correct Answer: (d) red
Solution:

Red. Wavelength is inversely proportional to the deviation in the path of the light. The color red, therefore, deviates the least since it has a maximum wavelength and the color violet deviates the most since it has the least wavelength.

3. The image (which we see on the screen) formed by the actual intersection of reflected rays is _____. [RRB Group D 05/12/2018 (Evening)]

Correct Answer: (d) real
Solution:

Real images can be obtained on the screen. Examples - The images formed on a cinema screen are real images. The virtual image is formed due to the apparent intersection of reflected or refracted light rays. Virtual images can’t be obtained on the screen. Example - The image of our face in a plane mirror is a virtual image.

4. What is the distance between the polar point or focus point and the center of vision or optic center in the lens called ? [RRB Group D 07/12/2018 (Evening)]

Correct Answer: (c) focal length or polar distance
Solution:

Focal length or polar distance. Principal focus is a point (on the principal axis) where parallel incident rays meet after reflecting (in mirrors) or refracting (in lenses). Focus is just a random point where some rays meet, it might be at the principal focus or otherwise. It also need not be placed on the principal axis of the lens/mirror.

5. If an object is placed at infinity, what will be the position of its image formed by a convex lens ? [RRB Group D 11/12/2018 (Evening)]

Correct Answer: (a) At the focus or center of F₂
Solution:

If an object is at infinity, the position of an image formed due to the convex lens is at the focal point. Convex lenses converge parallel rays coming from objects at infinity and a highly diminished - point sized, real and inverted image is formed at principal focus.

6. Which of the following mirrors always forms virtual and erect images and shows the size of the image equal to the size of the object ? [RRB Group D 14/12/2018 (Evening)]

Correct Answer: (d) plane mirror
Solution:

Plane mirror - A plane mirror is a mirror with a flat (planar) reflective surface. Characteristics of an image formed in a plane mirror - Image formed by a plane mirror is always virtual and erect; The size of the image is equal to that of the object; The image formed is as far behind the mirror as the object is in front of it; The image is laterally inverted.

7. The reflector of a searchlight is a: [RRB ALP Tier - I (09/08/2018) Morning]

Correct Answer: (c) concave mirror
Solution:

Concave Mirror: Reflecting surface is toward the center of the curvature. It is also known as a converging mirror. Image formed - Real, Virtual, Erect and Inverted. Uses: Shaving mirrors, Headlights and Solar furnaces.

8. A convex mirror of focal length f (in air) is immersed in a liquid ((μ = 4/3) The focal length of the mirror in liquid will be: [RRB ALP Tier - I (09/08/2018) Morning]

Correct Answer: (b) f
Solution:

f. The focal length of a mirror does not depend on the refractive index of the medium. On immersing a mirror in water, the focal length of the mirror remains unchanged because the focal length of the mirror depends on radius of curvature which is unchanged. So the focal length of the mirror is “f”.

9. If you look into a mirror and find that the image (your reflexion) is smaller than you, then the type of the mirror is: [RRB ALP Tier - I (09/08/2018) Afternoon]

Correct Answer: (b) convex mirror
Solution:

Convex mirror (Fish eye mirror or diverging mirror): It is that mirror whose reflecting surface is away from the center of the curvature. Image formed - Virtual and erect. Uses - Rear-view mirrors in vehicles, Security purposes in buildings and ATMs.

10. A person holding a pen in his left hand sees his reflection in the mirror holding the pen in his right hand. This is due to which of the following phenomena? [RRB ALP Tier - I (09/08/2018) Evening]

Correct Answer: (d) Lateral inversion
Solution:

Lateral inversion - It means the apparent reversal of the mirror image's left and right when compared with the object. Total internal reflection is the complete reflection of a light ray within the medium (Air, Water Glass). Refraction is the bending of a wave when it enters a medium where its speed is different.