NCERT Solutions Class 12 Physics Chapter 7 - Alternating Current

The physics chapter for Class 12 on alternating current (AC) follows the work done in previous chapters on electromagnetic induction and expands into the concept of alternating current (AC). The chapter discusses how AC can theoretically be defined and gives students a mathematical understanding of AC through angle (or phasors) and how AC takes place in the electrical components of a circuit. 

To develop a strong understanding of this chapter, it is necessary for students to understand Electrical Engineering (also called Modern Electricity), Resonance (Communication Systems), and Electrical Distribution (Power Transmission). Therefore, this chapter will be an important one for the CBSE Boards, JEE, and NEET. Additionally, the NCERT solutions for Chapter 7 provide students with many examples that demonstrate the phase relationships between voltage and current using both analytical methods and phasor diagrams. The early examples provided by these solutions are based on much simpler circuits, whereas the later examples are based on more complex series of LCR circuits.

1.0Download NCERT Solutions Class 12 Physics Chapter 7 Alternating Current: Free PDF

In order to understand Alternating Current, a good amount of understanding in Rotating Vectors (or Phasors) as well as Trigonometry will help considerably. The NCERT solutions for alternating currents outline all the textbook exercises from beginning to end, including calculating the Power Factor; Resonant Conditions and Transformer Efficiency. Students may also download these PDF versions of the NCERT solutions to learn about RMS Values and Impedance, which will enable them to correctly and accurately solve complex AC circuit problems.

2.0Class 12 Physics Chapter 7 Alternating Current: Key Concepts

This chapter focuses on the analysis of electrical components under time-varying voltage and the efficiency of power transfer. The key lessons include:

• RMS and Peak Values: Exploring how to relate the peak amplitude of alternating current (AC) and voltage with their root mean square value (or effective value) (rms).
• The application of AC voltage to a resistor, inductor and capacitor. There are phase shifts between current and voltage for all three devices; therefore the current and voltage for a resistor are in phase, while the current lags that of the voltage by a quarter of a cycle for an inductor, and conversely leads in a capacitor by a quarter of a cycle.
• The analysis of the combined effects of an inductor, a capacitor and a resistor in a series LCR circuit will lead to the determination of total impedance.
• The resonance of LCR circuits, or the frequency at which the total impedance is at a minimum and the total current is at its maximum, will lead to the concept of “Sharpness of Resonance” (Q-factor).
• Power in AC circuits: The derivation of “Wattless Current” and the significance of the Power Factor for electrical consumption.
• The type of oscillation that occurs between an inductor and a capacitor in an LC circuit will lead to a qualitative and quantitative understanding of the energy being exchanged between them.
• Transformers, which work on the principle of mutual induction to either step up or step down AC voltage, and the factors that may cause energy loss when a transformer is being operated.

3.0Key Features of NCERT Solutions for Class 12 Physics Chapter 7

• The solutions focus heavily on using phasor diagrams to visualize phase angle relationships, allowing students to better grasp the reason behind phase angle differences between the current that is "leading" or "lagging", without the need for rote memorization of phase relationships. 
• The solutions also include step-by-step Analyses of Resonance and Derivation of f_r and B_wp as well as an LCR circuit Breakthrough to further clarify the understanding of how LCR circuits work. 
• Quick reference tables are provided in The Solutions comparing the specifications of the different types of measuring instruments used to measure Resistance; either inductive or capacitive components and their relationships with frequency.
• In addition to proper explanations for the causes of transformer inefficiency such as Flux Leakage, Eddy Currents and Copper Losses (which have been asked in Board Exams), The Solutions also explain the reasons why they occur. 
• Finally, The Solutions provide a more thorough understanding of how to mathematically calculate circuit values ($V_l$, $V_c$ and $V_r$) using Vector Algebra through the use of the Pythagorean Theorem and the impedance triangle.