An EM wave from air enters a medium. The electric fields areE&rar

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 Multiple Choice QuestionsMultiple Choice Questions

11.

In a series resonant LCR circuit, the voltage across R is 100 volts and R = 1 kΩ with C = 2µF. The resonant frequency ω is 200 rad/s. At resonance the voltage across L is

  • 4 × 10−3 V

  • 2.5 × 10−2 V

  • 40 V

  • 40 V

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12.

Two voltameters one of copper and another of silver, are joined in parallel. When a total charge q flows through the voltameters, equal amount of metals are deposited. If the electrochemical equivalents of copper and silver are z1 and z2 respectively the charge which flows through the silver voltameter is

  • fraction numerator straight q over denominator 1 plus begin display style straight z subscript 1 over straight z subscript 2 end style end fraction
  • fraction numerator straight q over denominator 1 plus begin display style straight z subscript 2 over straight z subscript 1 end style end fraction
  • straight q straight z subscript 1 over straight z subscript 2
  • straight q straight z subscript 1 over straight z subscript 2
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13.

A circuit has a resistance of 12 Ω and an impedance of 15 Ω. The power factor of the circuit will be

  • 0.8

  • 0.4

  • 1.25

  • 1.25

174 Views

14.

The phase difference between the alternating current and emf is π/2. Which of the following cannot be the constituent of the circuit?

  • C alone

  • R.L

  • L.C

  • L.C

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15.

Alternating current can not be measured by D.C. ammeter because

  • A.C. cannot pass through D.C.

  • A.C. changes direction

  • average value of current for complete cycle is zero

  • average value of current for complete cycle is zero

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16.

In an LCR series a.c. circuit, the voltage across each of the components, L, C and R is 50 V. The voltage across the LC combination will be

  • 50 V

  • 50√2 V

  • 100 V

  • 100 V

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17.

In a LCR circuit capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to

  • 4L

  • 2L

  • L/2

  • L/2

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18.

For an RLC circuit driven with a voltage of amplitude vm and frequency ω0 = 1LC the current exhibits resonance. The quality factor, Q is given by:

  • CRω0

  • ω0LR

  • ω0RL

  • Rω0C


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19.

An EM wave from air enters a medium. The electric fields are

E1 = E01 x^ cos 2πvzc-t in air and E2 = E02 x^ cos [ k(2z-ct)] in medium, where the wave number k and frequency v refer to their values in air. The medium is non-magnetic. If εr1 and εr2refer to relative permittivities of air and medium respectively, which of the following options is correct ?

  • εr1εr2 = 12

  • εr1εr2 = 4

  • εr1εr2 = 2

  • εr1εr2 = 14


D.

εr1εr2 = 14

Velocity of EM wave is given by v = 1με

Velocity in air  = ωk =C

velocity in medium = C/2

Here, μ1 = μ2 =1 as medium is non magnetic

 1εr11εr2 = CC2 = 2εr1εr2 =14


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20.

If the rms value of sinusoidal input to a full wave rectifier is V0/2, then the rms value of the rectifier's output is

  • V0/2

  • V02/2

  • V02/2

  • 2 V02


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