Science (English Medium) Class 12 - CBSE Important Questions

 How are eddy currents produced ?

Describe briefly three main useful application of eddy currents ?

Welders wear special glass goggles while working. Why? Explain.

A toroidal solenoid with air core has an average radius of 15 cm, area of cross-section 12 cm² and has 1200 turns. Calculate the self-inductance of the toroid. Assume the field to be uniform across the cross-section of the toroid.

The currents flowing in the two coils of self-inductance L₁ = 16 mH and L₂ = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of induced voltages ?

The currents flowing in the two coils of self-inductance L₁ = 16 mH and L₂ = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of  the currents ?

The currents flowing in the two coils of self-inductance L₁ = 16 mH and L₂ = 12 mH are increasing at the same rate. If the power supplied to the two coil is equal, find the ratio of the energies stored in the two coils at a given instant ?

Figure shows a rectangular loop conducting PQRS in which the arm PQ is free to move. A uniform magnetic field acts in the direction perpendicular to the plane of the loop. Arm PQ is moved with a velocity v towards the arm Rs. Assuming that the arms QR, RS and SP have negligible resistances and the moving arm PQ has the resistance r, obtain the expression for (i) the current in the loop (ii) the force and (iii) the power required to move the arm PQ.

A light metal disc on the top of an electromagnet is thrown up as the current is switched on. Why? Give reason.

Predict the directions of induced currents in metal rings 1 and 2 lying in the same plane where current I in the wire is increasing steadily.

Define self-inductance of a coil. Show that magnetic energy required to build up the current I in a coil of self inductance L is given by `1/2 LI^2`

Predict the direction of induced current in a metal ring when the ring is moved towards a straight conductor with constant speed v. The conductor is carrying current I in the direction shown in the figure.

Predict the direction of induced current in metal rings 1 and 2 when current I in the wire is steadily decreasing?

A plot of magnetic flux (Φ) versus current (I) is shown in the figure for two inductors A and Β. Which of the two has larger value of self inductance?

Show diagrammatically how an alternating emf is generated by a loop of wire rotating in a magnetic field. Write the expression for the instantaneous value of the emf induced in the rotating loop.

Define self inductance. Write its S.I. units.

Derive an expression for self inductance of a long solenoid of length l, cross-sectional area A having N number of turns.

Explain, with the help of a suitable example, how we can show that Lenz's law is a consequence of the principle of conservation of energy.

Answer the following question.
When a conducting loop of resistance 10 Ω and area 10 cm² is removed from an external magnetic field acting normally, the variation of induced current-I in the loop with time t is as shown in the figure.
Find the
(a) total charge passed through the loop.
(b) change in magnetic flux through the loop
(c) magnitude of the field applied

A rectangular, a square, a circular and an elliptical loop, all in the (x - y) plane, are moving out of a uniform magnetic field with a constant velocity `vecv = vhati`. The magnetic field is directed along the negative z-axis direction. The induced emf, during the passage of these loops, out of the field region, will not remain constant for ______.