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

Figure shows a smooth pair of thick metallic rails connected across a battery of emf εhaving a negligible internal resistance. A wire ab of length l and resistance r can slide smoothly on the rails. The entire system lies in a horizontal plane and is immersed in a uniform vertical magnetic field B. At an instant t, the wire is given a small velocity vtowards right. (a) Find the current in it at this instant. What is the direction of the current? (b) What is the force acting on the wire at this instant? (c) Show that after some time the wire ab will slide with a constant velocity. Find this velocity.

V-I graph for a metallic wire at two different temperatures T1 and T2 is as shown in the figure. Which of the two temperatures is higher and why?

What is the ratio of the velocity of the wave in the two media of refractive indices μ1 and μ2?

A potential difference V is applied across a conductor of length L and diameter D. How is the drift velocity, v_d, of charge carriers in the conductor affected when (i) V is halved, (ii) L is doubled and (iii) D is halved ? justify your answer in each case.

The I-V characteristics shown in figure represent ______.

In an inertial frame of reference, the magnetic force on a moving charged particle is `vec"F"`. Its value in another inertial frame of reference will be ______.

Two-point charges placed in a medium of dielectric constant 5 are at a distance r between them, experience an electrostatic force ‘F’. The electrostatic force between them in vacuum at the same distance r will be ____________.

In a region of constant potential ______.

1. the electric field is uniform
2. the electric field is zero
3. there can be no charge inside the region
4. the electric field shall necessarily change if a charge is placed outside the region

A point charge q₀ is moving along a circular path of radius a, with a point charge Q at the centre of the circle. The kinetic energy of q₀ is ______.

Three-point charges Q, q and -q are kept at the vertices of an equilateral triangle of side L as shown in the figure. What is 

1. the electrostatic potential energy of the arrangement? and
2. the potential at point D?

State the principle of a cyclotron.

Show that the time period of revolution of particles in a cyclotron is independent of their speeds. Why is this property necessary for the operation of a cyclotron?

Derive the expression of Brewster's law when unpolarised light passing from a rarer to a denser medium gets polarised on reflection at the inteface.

State the underlying principle of a cyclotron. Write briefly how this machine is used to accelerate charged particles to high energies

Deduce an expression for the frequency of revolution of a charged particle in a magnetic field and show that it is independent of velocity or energy of the particle.

You are given prisms made of crown glass and flint glass with a wide variety of angles. Suggest a combination of prisms which will

(a) deviate a pencil of white light without much dispersion,

(b) disperse (and displace) a pencil of white light without much deviation.