How Power Actually Works in an AC LR Circuit (Full Derivation) class XII Physics NCERT CH.7

In this lecture (Class 12 Physics, Chapter 7: Alternating Current), Surendra Sir explains the step-by-step mathematical derivation of Average Power in an AC Circuit (Inductive / LR Circuit). Learn how instantaneous power, trigonometric identities, integration over a full AC cycle, and the concept of Power Factor ($\cos\phi$) come together to find total power dissipation. Essential topic for CBSE/State Board Exams, JEE Main, and NEET aspirants! ⏱️ Timestamps / Chapters 00:00 - Introduction to Lecture 09: Power in AC Circuit 02:08 - AC Circuit with Inductive Load (LR Circuit Setup) 02:44 - Instantaneous Voltage & Current Equations 03:28 - Instantaneous Power ($P = e \cdot i$) & Trigonometric Expansion 07:11 - Converting to Single Cosine Terms 10:13 - Work Done ($dW = P \cdot dt$) for Small Time Interval 12:46 - Integrating over Full Cycle ($0$ to $T$) 17:08 - Solving Limits & Eliminating Zero Terms 18:43 - Derivation of Average Power ($P_{\text{avg}} = \frac{E_0 I_0}{2} \cos\phi$) 19:28 - Average Power in RMS Terms ($P_{\text{avg}} = E_{\text{rms}} I_{\text{rms}} \cos\phi$) 20:25 - Understanding Power Factor ($\cos\phi$) & Impedance Form 22:08 - Summary & Upcoming Topics (Transformers, Numerical Problems) 📌 Don't forget to Like, Share, and Subscribe to Apex Study Centre Bageshwar for complete Class 11 & 12 Physics preparation! Drop your doubts in the comments below. Hashtags #Class12Physics #AlternatingCurrent #PowerInACCircuit #PhysicsDerivations #JEEMainPhysics #NEETPhysics #CBSEClass12 #ApexStudyCentre