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

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.

Five long wires A, B, C, D and E, each carrying current I are arranged to form edges of a pentagonal prism as shown in figure. Each carries current out of the plane of paper.

1. What will be magnetic induction at a point on the axis O? AxisE is at a distance R from each wire.
2. What will be the field if current in one of the wires (say A) is switched off?
3. What if current in one of the wire (say) A is reversed?

What are the dimensions of χ, the magnetic susceptibility? Consider an H-atom. Guess an expression for χ, upto a constant by constructing a quantity of dimensions of χ, out of parameters of the atom: e, m, v, R and µ₀. Here, m is the electronic mass, v is electronic velocity, R is Bohr radius. Estimate the number so obtained and compare with the value of |χ| ~ 10^–5 for many solid materials.

The mutual inductance M₁₂ of coil 1 with respect to coil 2 ______.

1. increases when they are brought nearer.
2. depends on the current passing through the coils.
3. increases when one of them is rotated about an axis.
4. is the same as M₂₁ of coil 2 with respect to coil 1.

There are two coils A and B seperated by some distance. If a current of 2A flows through A, a magnetic flux of 10^-2 Wb passes through B (no current through B). If no current passes through A and a current of 1A passes through B, what is the flux through A?