Alternating Current, Voltage & Terminologies| ALTERNATING CURRENT Physics 12 | Ch 20 | NBF | FBISE

Alternating Current, Voltage & Terminologies| ALTERNATING CURRENT Physics 12 | Ch 20 | National Book Foundation | Federal board

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In this lecture, we explore *Sinusoidal Alternating Current and Voltage* in detail, as per the **FBISE & Punjab Board Physics Class 12 curriculum (NBF Book)**. This topic is essential to understand how AC systems function in real-world applications, such as electricity supply and AC generators.

🔹 *Sinusoidal Alternating Current / Voltage:*
An AC generator produces the current or voltage of the form:
x = x₀ sin(ωt)
Here, x is the instantaneous value of current or voltage.
x₀ is the *peak (maximum)* value.
ω is the **angular frequency**.
For current: I = I₀ sin(ωt)
For voltage: V = V₀ sin(ωt)

The waveform is a **sine wave**, generated by rotating a coil in a magnetic field. This waveform:
✔ Changes polarity regularly
✔ Varies smoothly in magnitude
✔ Crosses zero rapidly and peaks slowly

🔹 *AC Terminologies Explained:*
*Cycle:* One complete waveform of positive and negative values
*Time Period (T):* Time for one full cycle
*Frequency (f):* Number of cycles per second (Hertz)
*Average Value:* Not used in power calculations for sine waves, since average over one cycle is zero
*Peak Value (x₀):* The highest positive/negative value in a cycle
*Root Mean Square (RMS) Value:* Equivalent DC value producing same heat:
I_rms = I₀ / √2
V_rms = V₀ / √2
RMS value is used in practical power ratings.

🔹 *Power in AC Circuits:*
Mean (average) power in a resistive load is:
P = (1/2) I₀² R
This shows that average power is *half* of maximum power in purely resistive AC circuits.

📚 This video is ideal for:
Class 12 Physics students (FSc Part 2)
Students of FBISE / Punjab Boards
MDCAT & ECAT aspirants
Anyone needing conceptual clarity on *AC physics*

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