Phase Of A.C through RESISTOR, INDUCTOR & CAPACITOR| Physics 12 | Ch 20 ALTERNATING CURRENT | FBISE

Phase Of A.C through RESISTOR, INDUCTOR & CAPACITOR| Physics 12 | Ch 20 ALTERNATING CURRENT | Federal Board | National Book Foundation
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Learn the *Phase difference of AC* through Resistor, Inductor, and Capacitor from Chapter 20 (Alternating Current) of Physics Class 12 (FBISE). This lecture explains how current and voltage behave differently in AC circuits and introduces the concepts of **inductive and capacitive reactance**, with phasor diagrams and mathematical relations. Understand how voltage leads or lags current in each case.

Key Concepts Covered:
Phase Difference in AC Circuits

In *alternating current (AC)* circuits, the **voltage and current are not always in phase**—meaning they don’t reach their maximum and minimum values at the same time. This difference in timing is called **phase difference**, and it's important for understanding how power flows in AC systems.

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🔁 *Voltage & Current Relationship in Inductor*

In a **pure inductor**, the **current lags the voltage by 90°**. This is because the inductor opposes the change in current due to its inductance. This behavior is summarized by the mnemonic **“ELI”**, where **E (voltage) leads I (current)**.

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⚡ *Voltage & Current Relationship in Capacitor*

In a **pure capacitor**, the **current leads the voltage by 90°**. The capacitor charges and discharges rapidly in response to voltage changes, making current flow before voltage builds up. This is captured by the mnemonic **“ICE”**, where **I (current) leads E (voltage)**.

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🧲 *Inductive Reactance (XL)*

The *inductive reactance* is the opposition offered by an inductor in an AC circuit. It depends on the frequency (f) of AC and inductance (L), and is given by the formula:
*XL = 2πfL*
Higher frequency = higher reactance.

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⚛️ *Capacitive Reactance (XC)*

The *capacitive reactance* is the opposition offered by a capacitor to the AC. It is inversely proportional to the frequency and capacitance (C):
*XC = 1 / (2πfC)*
Higher frequency = lower reactance.

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🧠 *Mnemonic: ELI the ICE Man*

A famous mnemonic to remember phase difference:

*ELI**: In an **Inductor (L)**, **E (voltage)* leads *I (current)*
*ICE**: In a **Capacitor (C)**, **I (current)* leads *E (voltage)*

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📈 *Phasor Diagrams*

Phasor diagrams help visualize the *phase difference* between voltage and current.

For **inductors**, the current arrow is 90° behind voltage.
For **capacitors**, the current arrow is 90° ahead of voltage.

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🔄 *AC Behavior vs DC*

In **DC circuits**, current is constant, so there’s **no phase difference**. In AC, because voltage and current continuously change, phase difference becomes essential, especially when analyzing **power, resonance, and impedance**.

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📎 *Hashtags:*
#ACPhaseDifference #Physics12 #FBISEPhysics #InductiveReactance #CapacitiveReactance #ELItheICEman #Chapter20Physics #AlternatingCurrent #Class12Physics #ACinCapacitorInductor


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