Electric Charges and Fields — Physics STD 12 Science — Question

In the adjoining circuit, the battery  has an e.m.f of 12 volt and zero internal resistance while the battery E has an e.m.f  of 2 volt. If the galvanometer G reads zero, then the value of the resistance X in ohm is

(a) 10

(b) 100

(c) 500

(d) 200

A particle is projected in a plane perpendicular to a uniform magnetic field. The area bounded by the path described by the particle is proportional to:

1. The velocity.
2. The momentum.
3. The kinetic energy.
4. None of these.

Four charges equal to – Q are placed at the four corners of a square and a charge q is at its centre. If the system is in equilibrium the value of q is

(a)

(b)

(c) -

(d)

Out of the following, the one whose frequency is minimum is:

An arc of a circle of radius R subtends an angle   at the centre. It carries a current i. The magnetic field at the centre will be

(a)

(b)

(c)

(d)

As shown in the figure, a magnet is moved with a fast speed towards a coil at rest. Due to this induced electromotive force, induced current and induced charge in the coil is E, I and Q  respectively. If the speed of the magnet is doubled, the incorrect statement is

(a) E increases

(b) I increases

(c) Q remains same

(d) Q increases

An electron is moving along the positive x-axis. You want to apply a magnetic field for a short time so that the electron may reverse its direction and move parallel to the negative x-axis. This can be done by applying the magnetic field along:

If the length of potentiometer wire is increased, then the length of the previously obtained balance point will

(a) Increase

(b) Decrease

(c) Remain unchanged

(d) Become two times

The energy band gap is maximum in

(a) Metals

(b) Superconductors

(c) Insulators

(d) Semiconductors