Electromagnetic Waves — Physics STD 12 Science — Question

The mutual inductance between a primary and secondary circuits is 0.5 H. The resistances of the primary and the secondary circuits are 20 ohms and 5 ohms respectively. To generate a current of 0.4 A in the secondary, current in the primary must be changed at the rate of

(a) 4.0 A/s

(b) 16.0 A/s

(c) 1.6 A/s

(d) 8.0 A/s

Figure given below shows two identical parallel plate capacitors connected to a battery with switch S closed. The switch is now opened and the free space between the plate of capacitors is filled with a dielectric of dielectric constant 3. What will be the ratio of total electrostatic energy stored in both capacitors before and after the introduction of the dielectric

(a) 3 : 1

(b) 5 : 1

(c) 3 : 5

(d) 5 : 3

Assertion  :   Faraday’s laws are consequences of conservation of energy.

Reason      : In a purely resistive ac circuit, the current lags behind the e.m.f. in phase.

(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 radius of curvature for a convex lens is 40 cm, for each surface. Its refractive index is 1.5. The focal length will be

(a) 40 cm

(b) 20 cm

(c) 80 cm

(d) 30 cm

Which of the following isotopes is normally fissionable ?

(a)

(b)

(c)

(d)

A watch glass containing some powdered substance is placed between the pole pieces of a magnet. Deep concavity is observed at the centre. The substance in the watch glass is:

An electron moving with a speed u along the positive x-axis at y = 0 enters a region of uniform magnetic field   which exists to the right of y-axis. The electron exits from the region after some time with the speed v at co-ordinate y, then

(a) v > u, y < 0

(b) v = u, y > 0

(c) v > u, y > 0

(d) v = u, y < 0

In NPN transistor the collector current is 10 mA. If 90% of electrons emitted reach the collector, then

(a) Emitter current will be 9 mA	(b) Emitter current will be 11.1 mA
(c) Base current will be 0.1 mA	(d) Base current will be 0.01 mA

The plate characteristic curve of a diode in space charge limited region is as shown in the figure. The slope of curve at point P is 5.0 mA/V. The static plate resistance of diode will be

(a) 111.1W

(b) 222.2W

(c) 333.3W

(d) 444.4W