Science (English Medium) Class 12 - CBSE Question Bank Solutions

Assertion: The earth¢s magnetic field is due to iron present in its core.

Reason: At a high temperature magnet losses its magnetism.

A dip circle is so set that its needle moves freely in the magnetic meridian. In this position, the angle of dip is 40º. Now the dip circle is rotated so that the plane in which the needle moves makes an angle of 30º with the magnetic meridian. In this position, the needle will dip by an angle ______.

The time period of oscillation of a magnet in a vibration magnetometer is 1.5 sec. The time period of oscillation of another magnet similar in size, shape and mass but having 1/4 magnetic moment than that of the 1st magnet oscillating at the same place will be ______.

The primary origin of magnetism lies in ______.

Which of the following is not showing the essential difference between electrostatic shielding by a conducting shell and magnetostatic shielding?

Two parallel plate capacitors X and Y, have the same area of plates and same separation between plates. X has air and Y with dielectric of constant 2, between its plates. They are connected in series to a battery of 12 V. The ratio of electrostatic energy stored in X and Y is ______.

In the circuit shown in figure, initially K₁ is closed and K₂ is open. What are the charges on each capacitors.

Then K₁ was opened and K₂ was closed (order is important), What will be the charge on each capacitor now? [C = 1µF]

Two charges q₁ and q₂ are placed at (0, 0, d) and (0, 0, – d) respectively. Find locus of points where the potential a zero.

The capacitors, each of 4 µF are to be connected in such a way that the effective capacitance of the combination is 6 µF. This can be achieved by connecting ______.

A capacitor of capacity C₁ is charged to the potential of V₀. On disconnecting with the battery, it is connected with an uncharged capacitor of capacity C₂ as shown in the adjoining figure. Find the ratio of energies before and after the connection of switch S.

Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel. What is the total capacitance of the combination?

Write clearly, why in the case of a transistor (i) the base is thin and lightly doped

Write clearly, why in the case of a transistor (ii) the emitter is heavily doped.

Obtain the expression for the energy stored per unit volume in a charged parallel plate capacitor.