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

Derive the expression for the torque acting on an electric dipole, when it is held in a uniform electric field. identify the orientation of the dipole in the electric field, in which it attains a stable equilibrium.

Answer the following question.

A cell of emf E and internal resistance r is connected across a variable resistor R. Plot the shape of graphs showing a variation of terminal voltage V with (i) R and (ii) circuit current I.

A conductor of length ‘l’ is rotated about one of its ends at a constant angular speed ‘ω’ in a plane perpendicular to a uniform magnetic field B. Plot graphs to show variations of the emf induced across the ends of the conductor with

1. angular speed ω and
2. length of the conductor l.

A short bar magnet of magnetic moment m = 0.32 J T^–1 is placed in a uniform magnetic field of 0.15 T. If the bar is free to rotate in the plane of the field, which orientation would correspond to its

1. stable, and
2. unstable equilibrium?

What is the potential energy of the magnet in each case?

If the solenoid is free to turn about the vertical direction and a uniform horizontal magnetic field of 0.25 T is applied, what is the magnitude of torque on the solenoid when its axis makes an angle of 30° with the direction of applied field?

A bar magnet of magnetic moment 1.5 J T ^–1 lies aligned with the direction of a uniform magnetic field of 0.22 T.

1. What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment:
   1. normal to the field direction,
   2. opposite to the field direction?
2. What is the torque on the magnet in cases (i) and (ii)?

A bar magnet of magnetic moment 1.5 J T^-1 lies aligned with the direction of a uniform magnetic field of 0.22 T.

What is the torque on the magnet in cases (i) and (ii)?

A circular coil of 16 turns and radius 10 cm carrying a current of 0.75 A rests with its plane normal to an external field of magnitude 5.0 × 10⁻² T. The coil is free to turn about an axis in its plane perpendicular to the field direction. When the coil is turned slightly and released, it oscillates about its stable equilibrium with a frequency of 2.0 s⁻¹. What is the moment of inertia of the coil about its axis of rotation?

A magnetic dipole is under the influence of two magnetic fields. The angle between the field directions is 60°, and one of the fields has a magnitude of 1.2 × 10^–2 T. If the dipole comes to stable equilibrium at an angle of 15° with this field, what is the magnitude of the other field?

Work done by a uniform electric field 'E' in moving a charge 'q' at a distance 'd' from a to b is ______.

If a current I is flowing in a straight wire parallel to x-axis and magnetic field is there in the y-axis then, ______.

According to Ampere's circuital law, ______.

Compass needle of magnetic moment m placed in a uniform magnetic field, experiences a torque equal to ______.

Magnetic potential energy U_m of compass needle of known magnetic moment m in a uniform magnetic field is ______.

A microscope is focussed on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?

What is the percentage of the mass of an atom concentrated in the nucleus?

Two cells of emfs approximately 5 V and 10 V are to be accurately compared using a potentiometer of length 400 cm.