In an L-C-R series circuit, at resonance from Physics Alternatin

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 Multiple Choice QuestionsMultiple Choice Questions

21.

The rms value of AC which when passed through a resistor produces heat, which is twice that produced by a steady current of 1.414 A in the same resistor is

  • 2 A

  • 3.46 A

  • 2.818 A

  • 1.732 A


22.

In a series LCR AC circuit, the current is maximum when the impedance is equal to

  • the reactance

  • the resistance

  • zero

  • twice the reactance


23.

A transformer connected to 220 V mains is used to light a lamp of rating 100 W and 110 V. If the primary current is 0.5 A, the efficiency of the transformer is ( approximately)

  • 60 %

  • 35 %

  • 50 %

  • 90 %


24.

A lamp consumes only 25 % of the peak power in an AC circuit. The phase difference between the applied voltage and the current is

  • π6

  • π3

  • π4

  • π2


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25.

In an L-C-R series circuit, at resonance

  • the current and voltage are in phase

  • the impedance is maximum

  • the current is minimum

  • the quality factor is independent of R


A.

the current and voltage are in phase

The condition for resonance, when ω = 1ωC,  then tan Φ = 0, that is, Φ = 0. In this case, the current (i) and voltage (V) are in phase.


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26.

A step-down transformer increases the input current 4 A to 24 A at the secondary. If the number of turns in the primary coil is 330, the number of turns in the secondary coil is

  • 60

  • 50

  • 55

  • 45


27.

An AC source of voltage E = 20 sin 100 t is connected across a resistance 20 Ω. The rms value of current in the circuit is

  • 1 A

  • 12 A

  • 12 A

  • 22 A


28.

In an L-C-R circuit

  • the impedance is equal to reactance

  • the ratio between effective voltage to effective current is called reactance

  • at resonance the net reactance is zero

  • at resonance the resistance is equal to the reactance


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29.

A step-down transformer with an efficiency of 80% is used on a 1000 V line to deliver 10 A at 100 V at the secondary coil. The current drawn from the line is

  • 1.5 A

  • 2 A

  • 3 A

  • 1.25 A


30.

Identify the wrong statement

  • Eddy currents are produced in a steady magnetic field

  • Eddy currents can be minimized by using laminated core

  • Induction furnace uses eddy current to produce heat

  • Eddy current can be used to produce breaking force in moving vehicles


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