Electrostatics — Physics STD 12 Science — Question

Which of the following is not a mode of radioactive decay?

A vector is not changed if:

1. It is rotated through an arbitrary angle.
2. It is multiplied by an arbitrary scalar.
3. It is cross multiplied by a unit vector.
4. It is slid parallel to itself.

Electric potential is equal to :

Assertion  :   Leclanche cell is used, when constant supply of electric current is not required.  

Reason     : The e.m.f. of a Leclanche cell falls, if it is used continuously.

(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.

The transfer ratio of a transistor is 50. The input resistance of the transistor when used in the common-emitter configuration is 1 KW. The peak value for an A.C input voltage of 0.01 V peak is

(a) 100 mA

(b) 0.01 mA

(c) 0.25 mA

(d) 500 mA

If mass-energy equivalence is taken into account, when water is cooled to form ice, the mass of water should:

Which among the following is false?

One face of a rectangular glass plate 6 cm thick is silvered.  An object held 8 cm in front of the first face, forms an image 12 cm behind the silvered face. The refractive index of the glass is

(a) 0.4

(b) 0.8

(c) 1.2

(d) 1.6

A convex lens is in contact with concave lens. The magnitude of the ratio of their focal length is 2/3. Their equivalent focal length is 30 cm. What are their individual focal lengths

(a) – 75, 50

(b) – 10, 15

(c) 75, 50

(d) – 15, 10