Science (English Medium) Class 12 - CBSE Important Questions for Physics

Obtain the expression for current sensitivity of moving coil galvanometer.

Two infinitely long straight parallel wires, '1' and '2', carrying steady currents I₁ and I₂ in the same direction are separated by a distance d. Obtain the expression for the magnetic field `vecB`due to the wire '1' acting on wire '2'. Hence find out, with the help of a suitable diagram, the magnitude and direction of this force per unit length on wire '2' due to wire '1'. How does the nature of this force changes if the currents are in opposite direction? Use this expression to define the S.I. unit of current.

Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage sensitivity. Explain, giving reason.

Define self-inductance of a coil.

State how a moving coil galvanometer can be converted into an ammeter.

How is current sensitivity increased?

In what way is Gauss's law in magnetism different from that used in electrostatics ? Explain briefly.

The Earth's magnetic field at the Equator is approximately 0.4 G. Estimate the Earth's magnetic dipole moment. Given : Radius of the Earth = 6400 km.

State Lenz's law. Illustrate, by giving an example, how this law helps in predicting the direction of the current in a loop in the presence of a changing magnetic flux.

In a given coil of self-inductance of 5 mH, current changes from 4 A to 1 A in 30 ms. Calculate the emf induced in the coil.

State any two causes of energy loss in actual transformers.

Derive the expression for the self-inductance of a long solenoid of cross sectional area A and length l, having n turns per unit length.

Draw a graph to show variation of capacitive-reactance with frequency in an a.c. circuit.

How are infrared waves produced?

How are X-rays produced?

Give any two uses of infrared waves.

A ray of light passes through an equilateral glass prism such that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of angle of prism. Find the angle of deviation.

Use Huygens' principle to show the propagation of a plane wavefront from a denser medium to a rarer medium. Hence find the ratio of the speeds of wavefronts in the two media.

Use the mirror equation to show that an object placed between f and 2f of a concave mirror produces a real image beyond 2f.

Use the mirror equation to show that a convex mirror always produces a virtual image independent of the location of the object.