Nuclei — Physics STD 12 Science — Question

A silver and zinc voltameter are connected in series and a current i is passed through them for a time t liberating W gm of zinc. The weight of silver deposited is nearly

(a) W

(b) 1.7 W

(c) 2.4 W

(d) 3.5 W

Assertion :  Electron has higher mobility than hole in a semiconductor.

Reason     : Mass of electron is less than the mass of hole.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

Two rays A and B being reflected by a mirror and going as A' and B'. The mirror:

1. Is plane.
2. Is convex.
3. Is concave.
4. May be any spherical mirror.

At a certain place a magnet makes 30 oscillations per minute. At another place where the magnetic field is double, its time period will be

(a) 4 sec

(b) 2 sec

(c)

(d)

If the field lines in a magnetic field are parallel and equidistant, the magnetic field is __________ .

The work function of a metal is:

A concave and convex lens have the same focal length of 20 cm and are put into contact to form a lens combination. The combination is used to view an object of 5 cm length kept at 20 cm from the lens combination. As compared to the object, the image will be

(a) Magnified and inverted

(b) Reduced and erect

(c) Of the same size as the object and erect

(d) Of the same size as the object but inverted

Force between two identical bar magnets whose centres are r metre apart  is 4.8 N, when their axes are in the same line. If separation is increased to 2r, the force between them is reduced to

(a) 2.4N

(b) 1.2N

(c) 0.6N

(d) 0.3N

A  cut diamond sparkles because of its

(a) Hardness	(b) High refractive index
(c) Emission of light by the diamond	(d) Absorption of light by the diamond