Electromagnetic Induction — Physics STD 12 Science — Question

An electric dipole is placed in a uniform electric field. The net electric force on the dipole.

When a negative charge is taken at a height from earth's surface, then its potential energy   

(a) Decreases	(b) Increases
(c) Remains unchanged	(d) Will become infinity

Electrical conductivity of a semiconductor

(a) Decreases with the rise in its temperature

(b) Increases with the rise in its temperature

(c) Does not change with the rise in its temperature

(d) First increases and then decreases with the rise in its temperature

A tuning fork of frequency 480Hz is used to vibrate a sonometer wire having natural frequency 410Hz. The wire will vibrate with a frequency.

1. 410Hz
2. 480Hz
3. 820Hz
4. 960Hz.

Electric field intensity at a point in between two parallel sheets with like charges of same surface charge densities (σ)  is

(a)

(b)

(c) Zero

(d)

Focal length of a convex lens will be maximum for

(a) Blue light

(b) Yellow light

(c) Green light

(d) Red light

The galaxies are moving away from each other. It is explained by

(a) White dwarf star

(b) Red shift

(c) Neutron star

(d) None of these

Sodium has body centred packing. If the distance between two nearest atoms is 3.7 Å, then its lattice parameter is

(a) 4.8 Å

(b) 4.3 Å

(c) 3.9 Å

(d) 3.3 Å

We have two wires A and B of same mass and same material.  The diameter of the wire A is half of that B.  If the resistance of wire A is 24 ohm then the resistance of wire B will be

(a) 12 Ohm

(b) 3.0 Ohm

(c) 1.5 Ohm

(d) None of the above

LED is a p-n junction diode which is: