Important Questions of Alternating Current Physics | Zigya

Previous Year Papers

Download Solved Question Papers Free for Offline Practice and view Solutions Online.

Test Series

Take Zigya Full and Sectional Test Series. Time it out for real assessment and get your results instantly.

Test Yourself

Practice and master your preparation for a specific topic or chapter. Check you scores at the end of the test.
Advertisement

 Multiple Choice QuestionsMultiple Choice Questions

Advertisement
41.

A transformer of efficiency 90% draws an input power of 4  kW. An electrical appliance connected across the secondary draws a current of 6 A. The impedance of the device is

  • 60 Ω

  • 50 Ω

  • 80 Ω

  • 100 Ω


42.

The resonance frequency of the tank circuit of an oscillator when L = 10π2 mH and C = 0.04 µF are connected in parallel is

  • 250 kHz

  • 25 kHz

  • 2.5 kHz

  • 25 MHz


43.

An alternating voltage e = 200 sin 100 t is applied to a series combination R = 30 Ω and an inductor of 400 mH. The power factor of the circuit is

  • 0.01

  • 0.2

  • 0.6

  • 0.042


44.

A transformer has an efficiency of 80%. It is connected to a power input of 5 kW at 200 V. If the secondary voltage is 250 V, the primary and secondary currents are respectively

  • 25 A, 20 A

  • 20 A, 16 A

  • 25 A, 16 A

  • 40 A, 25 A


Advertisement
45.

When a DC voltage of 200 V is applied to a coil of self-inductance 23π H, a current of 1 A flows through it. But by replacing DC source with AC source of 200 V, the current in the coil is reduced to 0.5 A. Then the frequency of AC supply is 

  • 100 Hz

  • 75 Hz

  • 50 Hz

  • 30 Hz


46.

In a L-R circuit, the value of L is 0.4π H  and the value of R is 30 Ω. If in the circuit, an alternating emf of 200 V at 30 cycles/s is connected, the impedance of the circuit and current will be

  • 11.4 Ω, 17.5 A

  • 30.7 Ω, 6.5 A

  • 40.4 Ω, 5 A

  • 50 Ω, 4 A


47.

Which ofthe following statement is incorrect ?

  • In LCR series AC circuit, as the frequency of the source increases, the impedance of the circuit first decreases and then increases

  • If the net reactance of an LCR series AC circuit is same as its resistance, then the current lags behind the voltage by 45°

  • At resonance, the impedance of an AC circuit becomes purely resistive

  • At resonance in LCR series AC circuit, the potential drops across inductor and capacitor are equal m magnitude but opposite in sign


48.

If an alternating voltage is represented as E = 141 sin (628 t), then the rms value of the voltage and the frequency are respectively

  • 141 V, 628 Hz

  • 100 V, 50 Hz

  • 100 V, 100 Hz

  • 141 V, 100 Hz


Advertisement
49.

A step-down transformer is used on a 1000 V line to deliver 20 A at 120 V at the secondary coil. If the efficiency of the transformer is 80%, the current drawn from the line is  

  • 3 A

  • 30 A

  • 0.3 A

  • 2.4 A


50.

For the series LCR circuit shown in the figure, what is the resonance frequency and the amplitude of the current at the resonating frequency ?

          

  • 2500 rad s-1 and 52 A

  • 2500 rad s-1 and 5 A

  • 2500 rad s-1 and 52 A

  • 250 rad s-1 and 52 A


Advertisement