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.