Geometrical Optics — Physics STD 12 Science — Question

A varying current at the rate of 3 A/s in a coil generates an e.m.f. of 8 mV in a nearby coil. The mutual inductance of the two coils is

(a) 2.66 mH

(b) 2.66

(c) 2.66 H

(d) 0.266 H

Calculate the current through a lamp of 25w operating at 220v.

The power of convex lens of focal length 20 cm in dioptre is :

When the temperature of silicon sample is increased from 27℃  to 100℃, the conductivity of silicon will be

(a) Increased

(b) Decreased

(c) Remain same

(d) Zero

Two plates are at potentials –10 V and +30 V. If the separation between the plates be 2 cm. The electric field between them is

(a) 2000 V/m

(b) 1000 V/m

(c) 500 V/m

(d) 3000 V/m

The torque on a bar magnet due to the earth's magnetic field is maximum when the axis of the magnet is

(a) Perpendicular to the field of the earth

(b) Parallel to the vertical component of the earth's field

(c) At an angle of 33o with respect to the N-S direction

(d) Along the North-South (N-S) direction

A rod of a certain metal is 1.0 m long and 0.6 cm in diameter.  Its resistance is 3.0 ×   ohm.  Another disc made of the same metal is 2.0 cm in diameter and 1.0 mm thick.  What is the resistance between the round faces of the disc

(a) 1.35 ×   ohm

(b) 2.70 ×   ohm

(c) 4.05 ×   ohm

(d) 8.10 ×   ohm

Equipotentials at a great distance from a collection of charges whose total sum is not zero are approximately.

In electrolytes, the mobile charges are:

Huygen’s principle of secondary wavelets may be used to

(a) Find the velocity of light in vacuum

(b) Explain the particle behaviour of light

(c) Find the new position of the wavefront

(d) Explain photoelectric effect