Nuclei — Physics STD 12 Science — Question

A man cannot see clearly the objects beyond a distance of 20 cm from his eyes. To see distant objects clearly he must use which kind of lenses and of what focal length

(a) 100 cm convex

(b) 100 cm concave

(c) 20 cm convex

(d) 20 cm concave

A potentiometer has uniform potential gradient across it.  Two cells connected in series (i) to support each other and (ii) to oppose each other are balanced over 6m and 2m respectively on the potentiometer wire.  The e.m.f.’s of the cells are in the ratio of

(a) 1 : 2

(b) 1 : 1

(c) 3 : 1

(d) 2 : 1

A river is flowing from west to east at a speed of 5 metres per minute. A man on the south bank of the river, capable of swimming at 10 metres per minute in still water, wants to swim across the river in the shortest time. He should swim in a direction:

1. Due north.
2. 30° east of north.
3. 30° north of west.
4. 60° east of north.

By Huygen's wave theory of light, we cannot explain the phenomenon of

(a) Interference

(b) Diffraction

(c) Photoelectric effect

(d) Polarisation

An ice cube is suspended in vacuum in a gravity free hall. As the ice melts it.

1. Will retain its cubical shape.
2. Will change its shape to spherical.
3. Will fall down on the floor of the hall.
4. Will fly up.

 The rate of flow of electric charge through any cross-section of a conductor is known as __________.

A plano-convex lens of refractive index 1.5 and radius of curvature 30 cm is silvered at the curved surface. Now this lens has been used to form the image of an object. At what distance from this lens an object be placed in order to have a real image of the size of the object

(a) 20 cm

(b) 30 cm

(c) 60 cm

(d) 80 cm

A thin equiconvex lens is made of glass of refractive index 1.5 and its focal length is 0.2 m, if it acts as a concave lens of 0.5 m focal length when dipped in a liquid, the refractive index of the liquid is

(a)

(b)

(c)

(d)

The universal property among all substances is