Alternating Current -Important Questions & Preparation Tips

In this article you will get the clue that from where and how the questions are being framed from chapter Alternating Current


CBSE Class 12th physics chapter, Alternating Current obtains 04 Marks. Experts of offer the best practice material that covers all important questions so that students will not miss any portion while preparing for board exams or competitive exams. Consider the mentioned terms/questions at the time of studying.

  • Find the value of current flowing through the resistor connected with an alternating voltage source?
  • Explain why average current is zero in one complete cycle when connected to an a.c. source whereas average power is not zero?
  • What is the usefulness of the rms concept?
  • What would happen if the household appliances are supplied with the peak voltage more than 311 V?
  • Define phasor and phasor diagram?
  • Deduce the expression for current when an ac voltage is applied to an inductor?
  • How is the inductive reactance different from that of resistance?
  • Show that the average power supplied to an inductor over one complete cycle is zero?
  • Deduce the expression for current when an ac voltage is applied to a capacitor?
  • How is the inductive reactance different from that of capacitive reactance?
  • Explain the phasor diagram solution for the LCR circuit?
  • What are the disadvantages of using phasor diagram for LCR circuits?
  • Provide with an analytical solution for the LCR circuit?
  • Define wattles circuit and name the circuits which are wattles
  • Formula for average power dissipation
  • Differentiate between natural frequency and resonant frequency?
  • How is resonance useful in tuning of radio channels?
  • Deduce the sharpness and quality factor in an ac circuit?
  • Give the average power dissipated in an ac circuit? Also discuss the various cases.

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  • What is principle on which the metal detector works?
  • Deduce the total energy in an LC Circuit?
  • How is LC oscillation similar to the oscillation of attached springs?
  • What are the similarities between forced oscillations and driven LCR circuit?
  • Differentiate between step-up and step down transformer?
  • What kind of losses occurs in an actual transformer?
  • Explain with a phasor diagram, the differences between a resistor, an inductor and a capacitor?

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  • Why is sparking observed when an electric appliance is suddenly switched off?
  • A 60V, 10W lamp is to be used on AC source of 100V,60Hz. Calculate the inductance of the choke coil required to be put in series to run the lamp[. How much pure resistance should be used in place of the choke coil, so that the lamp may run on its rated voltage?
  • An AC source is connected to two circuits, as shown. Obtain the current through the resistance R at resonance in both the circuits?


  • How much current is drawn by the primary of a transformer which steps down 220V to 22V to operate a device having an impedance of 220Ώ?
  • Why is inductance more appropriate than a resistance to decrease alternating current?
  • A bulb and a capacitor are connected in series to a source of alternating current. What will happen on increasing the frequency of the current?
  • Why is it not possible to have electrolysis by AC?
  • What is the main advantage of AC over DC due to which AC is used?
  • How will you use a 100V, 50W bulb on 200V AC mains?
  • I=I0 e-t/T is the output current in a circuit where

            e= exponential

            t= time

            I0= peak current

            T=period, then find the average current

  • For V= 200 sin 100 л t. Find time after which voltage raise to RMS value from zero

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