Nuclei — Physics STD 12 Science — Question

Armature current in dc motor will be maximum when

(a) Motor has acquired maximum speed	(b) Motor has acquired intermediate speed
(c) Motor has just started moving	(d) Motor is switched off

The total work done on a particle is equal to the change in its kinetic energy:

1. Always.
2. Only if the forces acting on it are conservative.
3. Only if gravitational force alone acts on it.
4. Only if elastic force alone acts on it.

The curve between charge density and distance near P-N junction will be

(a)

(b)

(c)

(d)

Which of the following statements is incorrect about hysteresis

(a) This effect is common to all ferromagnetic substances

(b) The hysteresis loop area is proportional to the thermal energy developed per unit volume of the material

(c) The hysteresis loop area is independent of the thermal energy developed per unit volume of the material

(d) The shape of the hysteresis loop is characteristic of the material

Half life of a radioactive element is 10 days. The time during which quantity remains 1/10 of initial mass will be

(a) 100 days

(b) 50 days

(c) 33 days

(d) 16 days

A charge q is located at the centre of a cube. The electric flux through any face is

(a)

(b)

(c)

(d)

The maximum magnification that can be obtained with a convex lens of focal length 2.5 cm is (the least distance of distinct vision is 25 cm)

(a) 10

(b) 0.1

(c) 62.5

(d) 11

Two parallel wires in free space are 10 cm apart and each carries a current of 10 A in the same direction. The force one wire exerts on the other per metre of length is

(a) 2 , attractive	(b) 2, repulsive
(c) 2  , attractive	(d) 2  , repulsive

During a negative beta decay:

1. An atomic electron is ejected.
2. An electron which is already present within the nucleus is ejected.
3. A neutron in the nucleus decays emitting an electron.
4. A proton in the nucleus decays emitting an electron.

Magnetic permeability is maximum for

(a) Diamagnetic substance	(b) Paramagnetic substance
(c) Ferromagnetic substance	(d) All of these