Science (English Medium) Class 12 - CBSE Important Questions

Assertion (A): On Increasing the current sensitivity of a galvanometer by increasing the number of turns may not necessarily increase its voltage sensitivity.

Reason (R): The resistance of the coil of the galvanometer increases on increasing the number of turns.

Select the most appropriate answer from the options given below:

Two concentric and coplanar circular loops P and Q have their radii in the ratio 2:3. Loop Q carries a current 9 A in the anticlockwise direction. For the magnetic field to be zero at the common centre, loop P must carry ______.

State the two Kirchhoff’s rules used in the analysis of electric circuits and explain them.

Derive the equation of the balanced state in a Wheatstone bridge using Kirchhoff’s laws.

Two long straight parallel conductors carrying currents I₁ and I₂ are separated by a distance d. If the currents are flowing in the same direction, show how the magnetic field produced by one exerts an attractive force on the other. Obtain the expression for this force and hence define 1 ampere.

Two long straight parallel current-carrying conductors are kept ‘a’ distant apart in the air. The direction of current in both the conductors is the same. Find the magnitude of force per unit length and the direction of the force between them. Hence define one ampere.

The given figure shows a long straight wire of a circular cross-section (radius a) carrying steady current I. The current I is uniformly distributed across this cross-section. Calculate the magnetic field in the region r < a and r > a.

In what way is the behaviour of a diamagnetic material different from that of a paramagnetic, when kept in an external magnetic field?

Which of the following substances are diamagnetic?

Bi, Al, Na, Cu, Ca and Ni

Which of the following substances are para-magnetic?

Bi, Al, Cu, Ca, Pb, Ni

The susceptibility of a magnetic material is − 2.6 × 10⁻⁵. Identify the type of magnetic material and state its two properties.

The relative magnetic permeability of a magnetic material is 800. Identify the nature of magnetic material and state its two properties.

Draw magnetic field line when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field line due to the substances?

An a-particle and a proton of the same kinetic energy are in turn allowed to pass through a magnetic field `vec"B"`, acting normal to the direction of motion of the particles. Calculate the ratio of radii of the circular paths described by them.

Answer the following question.
Define the term "Intensity" in the photon picture of electromagnetic radiation.

Identify the following magnetic materials :

If the magnetizing field on a ferromagnetic material is increased, its permeability ______.

A uniform magnetic field gets modified as shown in figure when two specimens A and B are placed in it.

(a)	(b)

1. Identify the specimen A and B.
2. How is the magnetic susceptibility of specimen A different from that of specimen B?

Which of the following cannot modify an external magnetic field as shown in the figure?

The relative magnetic permeability of a substance X is slightly less than unity and that of substance Y is slightly more than unity, then ______.