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Alternating Current

Alternating current (AC) is an electric current that changes magnitude and reverses direction periodically, contrasting with direct current (DC). AC is characterized by its sinusoidal wave form, with key values including RMS (0.707 times peak value) and average values that differ over half and full cycles. AC is generated using alternators and is widely used for power transmission due to its ability to be transformed between voltages efficiently.

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5 views2 pages

Alternating Current

Alternating current (AC) is an electric current that changes magnitude and reverses direction periodically, contrasting with direct current (DC). AC is characterized by its sinusoidal wave form, with key values including RMS (0.707 times peak value) and average values that differ over half and full cycles. AC is generated using alternators and is widely used for power transmission due to its ability to be transformed between voltages efficiently.

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jeestatecentre2025
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© © All Rights Reserved
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give me notes about alternating current

Alternating current (AC) is an electric current that continuously changes in magnitude and
periodically reverses its direction, unlike direct current (DC) that flows in one direction only. [1] [2]
[3]

Expression for AC: The instantaneous value of an alternating current is given by

where is the peak (maximum) value, is angular frequency, and is time. [2] [4] [1]
Frequency ( ) and Angular Frequency ( ): Frequency is the number of cycles per second.
Angular frequency is . [1]
AC Characteristics:
Magnitude and direction vary with time. In one half-cycle, the current flows in one
direction; in the next half-cycle, it reverses. [5]
Graphically, AC grows from zero to a maximum, returns to zero, then reverses, forming
a sinusoidal wave. [3]
Average (Mean) Value: The average value of AC over a half-cycle is 0.637 times the peak
value; over a full cycle, it is zero because the positive and negative halves cancel. [4] [2] [1]

RMS (Root Mean Square) Value: RMS value is 0.707 times the peak value. It is the value of
AC that delivers the same power to a resistor as a DC of equivalent value. [2]

AC Generation: Alternating current is produced using alternators or AC generators, which


operate on Faraday’s law of electromagnetic induction. [3]
AC Circuits:
Resistor only: Current and voltage are in phase.
Inductor only: Current lags voltage by 90° (inductive reactance).
Capacitor only: Current leads voltage by 90° (capacitive reactance). [4]
Reactance and impedance: Inductive reactance ( ), capacitive reactance (
), and overall opposition to AC is called impedance.
AC Power: In purely resistive circuits, average power is non-zero. In purely inductive or
capacitive circuits, average power consumed is zero (wattless current). [2]
Application: AC is commonly used for power transmission because it is easily transformed
from high to low voltages using transformers, reducing losses. [3]
These are the essential notes on alternating current for physics at the high school level. [5] [1] [4]
[2] [3]

1. https://www.askiitians.com/revision-notes/physics/alternating-current/
2. https://www.learncbse.in/alternating-current-cbse-notes-class-12-physics/
3. https://byjus.com/jee/alternating-current/
4. https://www.vedantu.com/content-files-downloadable/revision-notes/cbse-class-12-physics-notes-cha
pter-7-alternating-current.pdf
5. https://www.pw.live/concepts-alternating-current-circuits-theory-of-physics-class-12

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