Current Electricity — Physics STD 12 Science — Question

The fact that the conductance of some metals rises to infinity at some temperature below a few Kelvin is called

(a) Thermal conductivity	(b) Optical conductivity
(c) Magnetic conductivity	(d) Superconductivity

Three capacitors of capacitances 3 μF, 9μF  and 18 μF  are connected once in series and another time in parallel. The ratio of equivalent capacitance in the two cases will be

(a) 1 : 15

(b) 15 : 1

(c) 1 : 1

(d) 1 : 3

Which one of following is charge less ?

In a common emitter transistor, the current gain is 80. What is the change in collector current, when the change in base current is 250 mA

(a) 80  × 250 mA

(b) (250 – 80) mA

(c) (250 + 80) mA

(d) 250/80 mA

The value of angle of dip at the earth's magnetic pole is :

A ray of light incidents on a plane mirror at an angle of 30°.  The deviation produced in the ray is

(a) 30°

(b) 60°

(c) 90°

(d) 120°

If a spherical conductor comes out from the closed surface of the sphere then total flux emitted from the surface will be

(a)  (the charge enclosed by surface)	(b)  (charge enclosed by surface)
(c)   (charge enclosed by surface)	(d) 0

The half life period of a radioactive element X is same as the mean life time of another radioactive element Y. Initially both of them have the same number of atoms. Then

(a) X and Y have the same decay rate initially

(b) X and Y decay at the same rate always

(c) Y will decay at a faster rate than X

(d) X will decay at a faster rate than Y

A substance is behaving as convex lens in air and concave in water, then its refractive index is

(a) Smaller than air	(b) Greater than both air and water
(c) Greater than air but less than water	(d) Almost equal to water