NCERT Solutions for Class 12 Physics Chapter 7 – Alternating Current
NCERT Solutions for Class 12 Physics Chapter 7 – Alternating Current is one of those chapters where theory, mathematics, and application all come together. At Myclass24, we pay close attention to the way AC circuits are solved — using phasors, impedance, and resonance conditions — because students who master these tools score consistently well in both CBSE board exams and competitive entrance tests. Our solutions are written to make the mathematics of AC circuits feel systematic and approachable. Also, get subject-wise NCERT Solutions for class 12, for all chapters of Physics, check NCERT Solutions for class 12 Physics.
Find the PDF of NCERT Solutions for Class 12 Physics Chapter 7
The free PDF of NCERT Solutions for Class 12 Physics Chapter 7 – Alternating Current is available to download from Myclass24. This PDF includes all solved NCERT exercise problems along with phasor diagrams, impedance triangle illustrations, and resonance condition derivations. Students can use this PDF for both conceptual understanding and quick numerical practice during exam preparation.
Chapter 7 – At a Glance
Detail | Information |
Chapter Name | Alternating Current |
Chapter Number | 7 |
Class | Class 12 |
Subject | Physics |
Total Exercises | 2 (Exercise + Additional) |
Total Questions | 25 |
Important Topics | AC Circuits, Phasors, LCR Circuit, Resonance, Power Factor, Transformer |
CBSE Marks Weightage | Approx. 8 marks |
PDF Available | Yes – Free Download on Myclass24 |
What is Chapter 7 – Alternating Current About?
Chapter 7 introduces alternating current — a current that varies sinusoidally with time. Students first encounter the concepts of peak value and RMS (root mean square) value of AC voltage and current. The RMS value is particularly important because it represents the effective value that produces the same heating effect as an equivalent DC current.
The chapter then tackles AC circuits individually — a pure resistor, a pure inductor, and a pure capacitor — to understand how voltage and current are related in each case. In a resistor, they are in phase. In an inductor, current lags voltage by 90 degrees. In a capacitor, current leads voltage by 90 degrees. These phase relationships are best understood through phasor diagrams.
The LCR series circuit is the most important topic of this chapter. Students derive the expression for impedance and learn to use the impedance triangle. The condition for resonance in an LCR circuit — when inductive and capacitive reactances cancel each other — gives minimum impedance and maximum current. Resonant frequency, quality factor (Q factor), and bandwidth are key derived quantities.
Power in AC circuits introduces the concept of the power factor — the cosine of the phase angle between voltage and current. Only the resistive component consumes power; purely inductive and capacitive components are said to be wattless. The transformer — a device based on mutual inductance — is discussed with its working principle, ideal transformer equations, and energy losses.
Scoring Strategy for Chapter 7 in Board Exams
Chapter 7 consistently delivers high-value questions in the CBSE board exam. The derivation of impedance for an LCR circuit, the resonance condition, and transformer equations are nearly guaranteed five-mark questions. Power factor problems are common two and three-mark questions.
Students often struggle with phasor diagrams because they try to memorise them without understanding the underlying phase relationships. At Myclass24, our solutions build phasor diagrams from first principles every time, so students understand what each component represents rather than just copying a diagram.
FAQs on NCERT Solutions Class 12 Physics Chapter 7 –Alternating Current
Alternating current is an electric current that changes magnitude and direction periodically, whereas direct current flows in only one direction. This chapter explains the characteristics of alternating current, including frequency, amplitude, and time period. Students learn why alternating current is preferred for large-scale power transmission. Understanding the differences between AC and DC helps explain the functioning of household electricity systems and electrical appliances. Questions comparing these two forms of current are commonly included in examinations because they are fundamental to electrical engineering and modern power distribution.
The root mean square value of alternating current represents the equivalent direct current that produces the same heating effect in a resistor. This concept is important because AC continuously changes its value. The chapter explains how RMS values are calculated and why they are used in practical electrical measurements. Students learn to solve numerical problems involving voltage and current ratings. Understanding RMS values helps interpret power specifications of electrical devices and improves conceptual clarity regarding alternating current systems used in homes and industries.
Inductors and capacitors affect alternating current differently from direct current. Inductors oppose changes in current, while capacitors oppose changes in voltage. This chapter explains inductive reactance, capacitive reactance, and their dependence on frequency. Students learn how these components influence current flow and phase relationships in AC circuits. Understanding their behavior is important for solving numerical questions and analyzing electrical systems. These concepts are widely used in communication devices, filters, and power circuits, making them significant topics in examinations.
Resonance occurs when inductive reactance becomes equal to capacitive reactance in an AC circuit. At resonance, the circuit allows maximum current to flow and behaves as a purely resistive circuit. This chapter explains resonance frequency, circuit behavior, and practical applications. Students learn how resonance is used in radio receivers, communication systems, and tuning circuits. Understanding resonance is important because it demonstrates how electrical systems can be optimized for specific frequencies. Numerical and conceptual questions related to resonance are frequently asked in board and competitive examinations.