This Class 12 Physics worksheet on Alternating Current, along with its detailed solutions, is designed mainly for CBSE board exam preparation and MCQ-based revision. The worksheet contains 75 multiple-choice questions, all framed strictly from NCERT concepts. It covers alternating emf and current, rms and peak values, reactance and impedance, LCR series circuits, resonance, power and power factor, transformers, choke coils, and energy stored in inductors. The solutions explain each answer step by step, making the worksheet useful not just for practice but also for strengthening conceptual clarity.
I am writing about this worksheet because Alternating Current is one of those chapters where students remember formulas but still lose marks due to poor interpretation. Confusion usually arises in phase difference, resonance conditions, transformer relations, and rms versus peak values. A solution-based worksheet like this helps bridge that gap. By carefully analysing these MCQs, students can clearly see how NCERT theory is converted into one-mark numerical and conceptual questions, and where examiners usually test fundamentals.
Structure of the Alternating Current Worksheet
The worksheet consists of 75 MCQs, each carrying one mark, followed by a detailed solution section. The questions include direct concept-based MCQs, numerical problems, and logic-based reasoning questions. Many questions look lengthy but can be solved quickly if core concepts are clear.
The overall difficulty level ranges from moderate to high, making this worksheet ideal for revision after completing the chapter.
RMS Value, Peak Value and AC Basics
A significant number of questions test the fundamentals of alternating current, including:
- Relationship between peak value and rms value
- Average value of AC over a complete cycle
- Instantaneous value of current and voltage
- Interpretation of sinusoidal wave equations
These questions form the foundation of the chapter and are frequently asked in exams.
Reactance, Impedance and Phase Difference
Several MCQs focus on reactance and impedance in AC circuits. Students are tested on:
- Inductive and capacitive reactance
- Dependence of reactance on frequency
- Impedance of LCR series circuits
- Phase difference between current and voltage
These questions require conceptual clarity rather than memorisation.
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LCR Series Circuits and Resonance
A large portion of the worksheet is dedicated to LCR circuits. Questions include:
- Condition for resonance
- Behaviour of current and impedance at resonance
- Effect of changing L or C on resonant frequency
- Voltage across L, C and R at resonance
Resonance-based questions are high-weight and often repeated in exams.
Power and Power Factor in AC Circuits
The worksheet strongly emphasises power concepts in AC circuits. MCQs are based on:
- Average power in AC circuits
- Role of power factor
- Maximum power dissipation conditions
- Power consumption in resistive, inductive, and capacitive circuits
These questions test understanding of phase angle and its effect on power.
Transformers and Their Working
Transformers form a major section of the worksheet. Questions cover:
- Step-up and step-down transformers
- Turns ratio and voltage relation
- Current relation in primary and secondary
- Efficiency of transformers
- Core material and energy losses
These are direct scoring areas if NCERT theory is revised properly.
Choke Coils and Practical Applications
Several MCQs focus on choke coils and practical uses of AC, such as:
- Why choke coils reduce current without power loss
- Advantage of AC over DC in power transmission
- Domestic AC supply values in India
- Limitation of resistive methods of current control
These questions connect theory with real-life electrical systems.
Frequency Dependence and Circuit Behaviour
The worksheet includes questions on how AC circuits respond to frequency changes, including:
- Variation of reactance with frequency
- Impedance–frequency graph of LCR circuits
- Behaviour of circuit above and below resonance
Such questions test logical application of formulas.
