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 Multiple Choice QuestionsMultiple Choice Questions

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91.

The magnetic flux linked with a coil at any instant t is given by the equation : ϕ = 5t3 − 100t + 300. The magnitude of emf induced in the coil after 3 s is

  • 10 V

  • 20 V

  • 35 V

  • 70 V


92.

In 0.1 s, the current in a coil increases from 1 A to 1.5 A. If inductance of coil is 60 mH, then induced current in external resistance of 3Ω will be

  • 1 A

  • 0.5 A

  • 0.2 A

  • 0.1 A


93.

If a coil of 40 turns and area 4.0 cm2 is suddenly removed from a magnetic field, it is observed that a charge of 2.0 x 10-4 C flows into the coil. If the resistance of the coil is 80 Ω, the magnetic flux density in Wb/m2 is

  • 0.5

  • 1.0

  • 1.5

  • 2.0


94.

The magnetic flux linked with the coil varies with time as  ϕ = 3 t2 + 4 t + 9. The magnitude of the induced emf at 2 s is

  • 9 V

  • 16 V

  • 3 V

  • 4 V


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95.

A coil having an inductance of 0.5 H carries a current which is uniformly varying from 0 to 10 A in 2s. The emf (in volts) generated in the coil is

  • 10

  • 5

  • 2.5

  • 1.25


96.

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


97.

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


98.

The magnetic flux through a loop of resistance 10 Ω is given by (ϕ=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


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99.

The magnetic flux linked with a coil satisfies the relation ϕ = 4t2 + 6t + 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


100.

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 XC =XL is included in the same circuit

  • an iron rod is inserted in the coil


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