141.

Lenz's law of electromagnetic induction corresponds to the

• law of conservation of charge

• law of conservation of energy

• law of conservation of momentum

• law of conservation of angular momentum

The current through a coil of self-inductance L = 2mH is given by i = t²e^-t at time t. How long it will take to make the emf zero ?

• 1 s

• 2 s

• 3 s

• 4 s

The magnetic flux through a loop of resistance 10 Ω is given by ($\mathrm{\varphi }$=5t² − 4t+ 1 Wb). How much current is induced in the loop after 0.2 s ?

• 0.4 A

• 0.2 A

• 0.04 A

• 0.02 A

The magnetic flux linked with a coil satisfies the relation $\mathrm{\varphi } = 4{\mathrm{t}}^2 + 6\mathrm{t} + 9$  Wb, where t is the time in second. The emf induced in the coil at t = 2 s is

• 22 V

• 18 V

• 16 V

• 40 V

A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when

• frequency of the AC source is decreased

• number of turns in the coil is reduced

• a capacitance of reactance X_C =X_L is included in the same circuit

• an iron rod is inserted in the coil