Alternating Current – Physics 2026 Complete Guide

Alternating Current (AC) is one of the most important chapters from Electricity & Magnetism for Boards, JEE & NEET 2026.

At CHEMASH, we teach AC with deep derivations, resonance concepts, power factor understanding, and advanced numerical problem-solving in a low-budget trusted tuition model for all classes.

What is Alternating Current?
AC Voltage & Current Equation
RMS & Average Value
AC Circuits (R, L, C)
Impedance & Phase Angle
Resonance in RLC Circuit
Power in AC Circuit
Transformer
Solved Numericals
MCQs
FAQs

1️⃣ What is Alternating Current?

Alternating Current is the current which changes its magnitude and direction periodically with time.

AC is generated in power stations and supplied to homes (50 Hz in India).

2️⃣ AC Voltage & Current Equation

Instantaneous current:

i = I₀ sin ωt

I₀ = Peak current
ω = Angular frequency = 2πf

3️⃣ RMS & Average Value

Root Mean Square value:

I_rms = I₀ / √2

V_rms = V₀ / √2

Important for numerical problems in JEE & Boards.

4️⃣ AC Circuits (R, L, C)

Pure Resistor:

Voltage & current in same phase

Pure Inductor:

Current lags voltage by 90°

Pure Capacitor:

Current leads voltage by 90°

5️⃣ Impedance & Phase Angle

Impedance:

Z = √(R² + (X_L − X_C)²)

Reactances:

X_L = ωL X_C = 1/ωC

6️⃣ Resonance in RLC Circuit

Condition:

X_L = X_C

Resonant Frequency:

f = 1 / (2π√LC)

At resonance, impedance is minimum.

7️⃣ Power in AC Circuit

Average Power:

P = V_rms I_rms cosφ

cosφ = Power factor

8️⃣ Transformer

Used to step up or step down voltage.

V_s/V_p = N_s/N_p

9️⃣ Solved Numerical

Q: Peak voltage = 311V. Find RMS voltage.

V_rms = V₀/√2 = 311 / 1.414 ≈ 220V

🔟 MCQs (Exam 2026)

1. RMS value of AC is:
A) V₀
B) V₀/2
C) V₀/√2 ✔
D) 2V₀

2. At resonance impedance is:
A) Maximum
B) Minimum ✔
C) Infinite
D) Zero

FAQs

Is AC important for JEE 2026?
Yes. Resonance, impedance & power factor are frequently asked.

Does CHEMASH provide advanced AC numericals practice?
Yes. Weekly test series & problem-solving sessions are provided.

Why Choose CHEMASH?

Affordable tuition for all classes
Experienced Physics teachers
Concept clarity + shortcut methods
Weekly mock tests
Trusted Science brand

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