Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

1 volt is equivalent to ______.

The work done in bringing a unit positive charge from infinite distance to a point at distance x from a positive charge Q is W. Then the potential at that point is ______.

Consider a uniform electric field in the z-direction. The potential is a constant ______.

The nature of parallel and anti-parallel currents are ______.

The earth behaves as a magnet with magnetic field pointing approximately from the geographic ______.

A solenoid is connected to a battery so that a steady current flows through it. If an iron core is inserted into the solenoid, the current will ______.

If number of turns in primary and secondary coils is increased to two times each, the mutual inductance ______.

By increasing the temperature, the specific resistance of a conductor and a semiconductor -

We use alloys for making standard resistors because they have ____________.

Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon the ______.

Three infinitely long parallel straight current-carrying wires A, B and C are kept at equal distance from each other as shown in the figure. The wire C experiences net force F. The net force on wire C, when the current in wire A is reversed will be ______.

In a hydrogen atom the electron moves in an orbit of radius 0.5 A° making 10 revolutions per second, the magnetic moment associated with the orbital motion of the electron will be ______.

• Assertion (A): An electron has a high potential energy when it is at a location associated with a more negative value of potential, and a low potential energy when at a location associated with a more positive potential.
• Reason (R): Electrons move from a region of higher potential to region of lower potential.

Select the most appropriate answer from the options given below:

In the circuit shown in figure initially, key K₁ is closed and key K₂ is open. Then K₁ is opened and K₂ is closed (order is important). [Take Q₁′ and Q₂′ as charges on C₁ and C₂ and V₁ and V₂ as voltage respectively.]

Then

1. charge on C₁ gets redistributed such that V₁ = V₂
2. charge on C₁ gets redistributed such that Q₁′ = Q₂′
3. charge on C₁ gets redistributed such that C₁V1 + C₂V₂ = C₁E
4. charge on C1 gets redistributed such that Q₁′ + Q₂′ = Q

Calculate potential energy of a point charge – q placed along the axis due to a charge +Q uniformly distributed along a ring of radius R. Sketch P.E. as a function of axial distance z from the centre of the ring. Looking at graph, can you see what would happen if – q is displaced slightly from the centre of the ring (along the axis)?

1. In a quark model of elementary particles, a neutron is made of one up quarks [charge (2/3) e] and two down quarks [charges –(1/3) e]. Assume that they have a triangle configuration with side length of the order of 10^–15 m. Calculate electrostatic potential energy of neutron and compare it with its mass 939 MeV.
2. Repeat above exercise for a proton which is made of two up and one down quark.

Temperature dependence of resistivity ρ(T) of semiconductors, insulators and metals is significantly based on the following factors:

1. number of charge carriers can change with temperature T.
2. time interval between two successive collisions can depend on T.
3. length of material can be a function of T.
4. mass of carriers is a function of T.

Do magnetic forces obey Newton’s third law. Verify for two current elements dl₁ = dlî located at the origin and dl₂ = dlĵ located at (0, R, 0). Both carry current I.