Xam Idea Class 12 Physics Chapter 7 Solutions: Alternating Current

Xam Idea Class 12 Physics Solutions for Chapter 7 ‘Alternating Current’ is a very handy resource that will help you solve all the problems associated with this chapter. This chapter of Xam Idea solutions will introduce you to the AC (alternating current), its transmissions and derivatives. You will understand the AC current and voltage representations by the Phasor diagrams, AC voltage applied to capacitors and series LCR circuit, resonance,  along with LC oscillations. Graphical illustrations and phasor diagrams make this chapter more interesting in learning.

Xam Idea Class 12 Physics Solutions for Alternating Current have 80 problems with their effective solutions. These problems are structured in three sections named Very Short Answer Type, Short Answer Type I & II, and Long Answer Type, respectively. They are based on the important topics that are included in this chapter. With these questions, you will be able to find the capacitive reactance, power factor, wattless current, power dissipated in the circuit, RMS value of current and voltage, angular frequency, and many more things.

Our Xam Idea Physics Solutions are the best practice material available here to help you revise the concepts of Alternating Current easily. Our subject experts have made these solutions in a manner that will help you remember the concepts over a long period. They are easy to access and to comprehend the topics. It is necessary to practice with Xam Idea solutions because many times it has been observed that similar questions are asked in CBSE Class 12 board exams.

Important Topics of Xam Idea Class 12 Physics Solutions Chapter 7: Alternating Current

This chapter focuses on AC and its transmissions. We here will discuss some beautiful and important concepts associated with it, that can help you understand each and everything about Alternating current.

What is Alternating Current?

Unlike DC (Direct Current) which flows only in a single direction, the Alternating current is a type of electric current that flows in both directions means it changes its direction after a certain period. Not only AC but also AC voltage changed direction with a period. It is usually represented as sine waves, however sometimes in triangular and rectangular waves also.

Alternating current is the most commonly used currently in a daily life basis. It is delivered to your houses, buildings, offices, etc.

Let’s have a look at some of the most widely used applications of alternating current-

  • In India, it has been depicted that most of the television sets use 220 AC power supply.
  • It generates the AC power from the DC source Batteries with the help of electronic device Inverter.
  • It’s been widely used in appliances like microwaves, refrigerators, toasters, dishwashers, and so on.
  • Used in Radio as well.

Alternating Current and Voltage By Rotating Vectors-Phasors

We have seen in AC circuits, the resistor, inductors, capacitors are usually connected in series and sometimes parallel also. You know, the Resistors are in the same phase as the voltage source. However, the Inductors or Capacitors can either be ‘lag’ or ‘leads’ behind the voltage source. That’s why we have a phasor-diagram to relate the current and voltage source.


  • Phasors are used to describe the relation between voltage and current in the sinusoidal waveform. If we have two or more sinusoidal waves, having the same frequency, different amplitude, and phase, then we use a phasor diagram to represent the phase difference between the sinusoidal signals.
  • The magnitude of phasors is considered as a peak value of the voltage and current.
  • Phasors usually rotate in an anticlockwise direction.

Here, We have a general expression for representing sinusoidal waveform-

A(t)=Am sin(ωt+ϕ )

In this above expression, Am is the peak amplitude, ω is the angular frequency, and ϕ is phase-shift.

Now, here the graph is shown above clearly depicts that, as the vector rotates in the anticlockwise direction at a speed of rad/s, and if we take that projection along the Y-axis, then we will have an Instantaneous value of a voltage. Taking the dot values of them, we can represent the sinusoidal signal of the waveform.

When we have a Resistor in an Ac Circuit:

In this condition we will have, an average value of current  i avg = 0, and the RMS value of a current,  Irms = im / √2

Let’s have a look at some terminologies and concepts associated with an AC circuit-

  • Inductive Reactance-

It’s an opposition to a changing current flow, measured in ohms like resistance. A voltage leads the current in a purely inductive circuit.


  • Capacitive Reactance-


It’s just like a capacitance, opposes Alternating current, measured in farads like capacitors. A voltage lags behind the current in a pure conductive current.

  • Impedance-

Impedance is the effective resistance of an AC circuit that arises from the combined effects of ohmic resistance and reactance. It is denoted by Z.

Where, X = XL – Xc


  • Resonance-


It’s a state in an AC circuit, at which inductive reactance is equal to the capacitive reactance.

XL = Xc

  • Power Factor-

In simple words, the power factor is equal to the ratio of real power dissipated to the apparent power. It ranges from -1 to 1.

  • Wattless Current-

If we talk about the pure inductive or pure capacitive circuit, the power dissipated in the circuit is zero, it means no current will be flowing in the circuit, a current is called wattless current.

Exercise Discussion of Xam Idea Class 12 Physics Solutions Chapter 7: Alternating Current

There are 80 questions in Xam Idea Class 12 Physics Solutions for this chapter. Let’s see what you will learn from these question types-

Very Short Type Questions

  • We have a total of 15 questions that are divided into two sections named PYQ (previous year questions) and OIQ (objective inventory questions). The PYQ part has 9 questions and the OIQ part has 6 questions. These questions are simple to solve 
  • The PYQ part has questions based on the capacitive reactance, power factor, wattless circuits, transformers, and the characteristics properties of their materials. You need to just revise these concepts once, you will be able to handle these questions.
  • While the OIQ part consists of 6 questions. In one of the questions, you will be asked to find the RMS value of alternating current.
  • There will be a question at which you need to relate the frequency with capacitive and inductive reactance.

Short Answer Type Question I

  • Type I consists of around 24 questions of Alternating Current. 6 questions in the PYQ part whereas 18 questions are there in the OIQ part.
  • The questions in the PYQ part are based on the quality factor, Average value, the RMS value of current in LCR circuits.
  • In the OIQ part, there are 18 questions you need to solve. The questions are based on the Phasor-Diagram, power Dissipated, Resonant circuits, and so on.
  • In one of the questions, you will be given the Instantaneous current and voltage, and you have to find the Impedance and Wattless current.

 Apart from this, some reason based questions is also there in this section. Like, when the capacitor is connected in a series LCR circuit, the AC flowing in the circuit increases.

Short Answer Type Question- II

  • Type II has 26 questions. The PYQ part has 17 questions and the rest 9 are in the OIQ part.
  • In the PYQ part, you will have questions on Impedance, Power, current, capacitance, resonance, angular frequency, current at resonance, etc.
  • In the OIQ part, you will have a question at which you need to give a reason that, can a voltage across capacitance and Inductance be greater than the voltage of an AC source?

Long Answer Type Questions

  • Herein, you will have around 26 questions in total that will cover the entire concepts involved in this chapter.
  • You will have a graph-based question in this section, and at which you need to give the reason for all the components associated with the LCR circuit. The components are Ac voltage, Average Current, RMS current, and so on.
  • You will have a question on Ac generator, you need to describe the working of AC generators with a labelled diagram.

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  • Our Xam Idea solutions can be a great assistance for you to deal with the high order thinking problems of Alternating Current.
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