Alternating Current | Class 12 Physics Notes
By ConceptScroll Team · Published on 17 July 2026 · 2 min read
Alternating Current – this guide gives you a concise, exam-ready overview of Alternating Current from Class 12 Physics, written by ConceptScroll editors and reviewed against the latest NCERT textbook.
7.1 INTRODUCTION
This section introduces the fundamental concept of alternating current (AC) as distinct from direct current (DC). Direct current flows in a constant direction with a steady magnitude, whereas alternating current and voltage vary sinusoidally with time. The common electrical mains supply in homes and offices is an alternating voltage that varies like a sine function over time. The current driven by such a voltage is called alternating current (AC current). AC is preferred over DC for power transmission and distribution because AC voltages can be easily transformed from one voltage level to another using transformers, enabling economical transmission over long distances. AC circuits also exhibit unique characteristics exploited in many devices, such as radio tuning, where the frequency-selective properties of AC circuits are utilized. The section also notes the linguistic redundancy in the terms 'AC voltage' and 'AC current' but acknowledges their universal acceptance. The importance of AC in modern electrical energy systems is emphasized, setting the stage for detailed study of AC circuit behavior in subsequent sections.
📊 Diagram: See figure_1: NICOLA TESLA (1856 - 1943), the inventor who conceived the rotating magnetic field principle fundamental to AC machinery.
🔗 Connection: Leads to the next section which analyzes the behavior of AC voltage applied to a resistor, introducing the mathematical description of sinusoidal AC voltage and current.
Frequently asked questions
What is the resistance offered by a pure inductor for DC?
zero
If the power factor of LCR circuit is one then the circuit is purely
resistive
A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B. It is then bent into a circular loop of smaller radius, having ‘n’ turns. The magnetic field at the centre of the coil will be
n 2 B
When an AC is connected to a resistor what is the phase difference between the current and voltage?
0 0
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