Alternating Current (AC) is the type of electric current that changes its direction and magnitude continuously with time. It is widely used in homes, industries, and power transmission systems because it can be easily generated and transmitted over long distances.
In this unit, students learn about AC generation, RMS values, reactance, impedance, resonance, transformers, and power in AC circuits. These topics are very important for board exams and help students understand how electrical energy is supplied and used in real life.
These notes are prepared according to the Punjab Board syllabus and include MCQs, short questions, long questions, and important concepts for quick and effective revision.
📥 Download Class 12 Physics Unit 16 Alternating Current Notes
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✔ Complete Unit 16 Notes
✔ Important Definitions & Concepts
✔ Important Formulas
✔ MCQs with Answers
✔ Short Questions (Exam Based)
✔ Long Questions
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📝 MCQs – Alternating Current
1. Alternating current is the current which:
(a) Flows in one direction only
(b) Changes its magnitude only
(c) Changes its direction periodically ✅
(d) Remains constant
2. The frequency of AC used in Pakistan is:
(a) 25 Hz
(b) 40 Hz
(c) 50 Hz ✅
(d) 60 Hz
3. The time taken by AC to complete one cycle is called:
(a) Frequency
(b) Amplitude
(c) Time period ✅
(d) Phase
4. The unit of frequency is:
(a) Volt
(b) Ampere
(c) Hertz ✅
(d) Ohm
5. The opposition offered by an inductor to AC is called:
(a) Resistance
(b) Capacitance
(c) Inductive reactance ✅
(d) Conductance
6. The unit of impedance is:
(a) Volt
(b) Ampere
(c) Ohm ✅
(d) Henry
7. In a purely resistive AC circuit, current and voltage are:
(a) Out of phase
(b) 90° out of phase
(c) In phase ✅
(d) 180° out of phase
8. At resonance, impedance of RLC circuit is:
(a) Maximum
(b) Minimum ✅
(c) Zero
(d) Infinite
❓FAQs – Alternating Current (Unit 16)
Q1: What is Alternating Current (AC)?
Alternating Current (AC) is an electric current that continuously changes its direction and magnitude with time.
Q2: What is impedance in an AC circuit?
Impedance is the total opposition offered by resistance and reactance to the flow of alternating current.
Q3: Why are transformers important in AC systems?
Transformers are used to increase or decrease voltage levels, making power transmission efficient and safe.
Q4: Which topics are most important in Unit 16 Alternating Current?
Important topics include RMS value, reactance, impedance, resonance, power in AC circuits, and transformers.