Introduction to Alternating Current (AC)

The chapter Alternating Current (AC) is a vital part of NEET Physics under electrodynamics and circuits. It explains the characteristics of alternating current, voltage, and their behavior in R, L, and C circuits.

Understanding this chapter is crucial for NEET aspirants because it combines conceptual understanding, formula derivation, and applications, frequently appearing in both theory and numericals.

StudentBro notes provide exam-focused explanations, step-by-step derivations, and solved examples for mastery.

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Concept of Alternating Current

• Definition: An alternating current (AC) is a current that reverses its direction periodically.

• AC Voltage: V(t) = V₀ sin(ωt) or V₀ cos(ωt)

  • V₀ = peak voltage

  • ω = angular frequency

• Frequency (f): Number of cycles per second

• Time Period (T): T = 1/f

• NEET conceptual questions often include direction, period, and frequency of AC.

Instantaneous, Average, and RMS Values

1. Instantaneous Value: Value of current or voltage at a specific time

2. Average Value: Average over one half-cycle = 0.637 × peak value

3. RMS Value: Root mean square value = 0.707 × peak value

• RMS is used in power calculations in AC circuits

• NEET numericals often involve calculating RMS and peak values.

AC in Pure Resistor, Inductor, and Capacitor

1. AC in Resistor (R):

   • Current and voltage are in phase

   • I = V/R

2. AC in Inductor (L):

   • Voltage leads current by 90°

   • X_L = ωL (inductive reactance)

3. AC in Capacitor (C):

   • Current leads voltage by 90°

   • X_C = 1 / (ωC) (capacitive reactance)

• NEET numericals may ask phase difference, current, or voltage in R, L, C circuits.

AC in Series RLC Circuit

• Impedance (Z): Z = √(R² + (X_L − X_C)²)

• Phase Angle (φ): φ = tan⁻¹((X_L − X_C)/R)

• Current: I = V / Z

• Power: P = VI cosφ = I² R

• NEET questions may involve calculations of impedance, phase, and power.

Resonance in AC Circuits

• Condition: X_L = X_C

• Resonant Frequency: f_r = 1 / (2π√LC)

• Effect: Impedance is minimum, current is maximum

• Applications: Radio tuning, filters, and oscillators

• NEET conceptual questions often include resonance frequency and circuit behavior at resonance.

Power in AC Circuits

• Instantaneous Power: p(t) = v(t) × i(t)

• Average Power: P = VI cosφ

  • cosφ = power factor

• Power Factor: Ratio of active power to apparent power

• Importance: Energy efficiency in AC circuits and transformers

• NEET numericals may ask average power, instantaneous power, and power factor.

LC Oscillations

• Definition: Oscillations of charge and current in LC circuits without resistance

• Frequency of Oscillation: f = 1 / (2π√LC)

• Energy oscillates between electric field of capacitor and magnetic field of inductor

• NEET questions may include time period, maximum current, and energy distribution.

Applications of Alternating Current

1. AC Power Supply: Standard supply in homes and industries

2. Transformers: Step-up or step-down AC voltage efficiently

3. Resonance Circuits: Radio and TV tuning

4. AC Motors: Used in industries

5. Energy Transmission: Long-distance electricity transmission uses AC

• NEET may ask conceptual applications, calculations, or differences between AC and DC.

Tips for NEET Preparation on AC

1. Memorize formulas for RMS, reactance, impedance, power, resonance, and LC oscillations

2. Practice numericals involving phase angle, current, voltage, and power

3. Understand phase relationships in R, L, C, and RLC circuits

4. Relate concepts to practical devices like transformers, motors, and power grids

5. Solve both conceptual and formula-based questions for NEET readiness

StudentBro notes include diagrams, derivations, and solved examples for clear visualization of AC behavior and circuit analysis.

Advantages of StudentBro NEET Physics Notes

• Covers RMS and peak values, AC in R, L, C, series RLC, resonance, power, LC oscillations, and applications

• Includes step-by-step derivations, solved numericals, and real-life applications

• Structured for easy revision and conceptual clarity

• Focused on NEET syllabus and high-yield questions

These notes ensure aspirants can confidently tackle alternating current questions in NEET exams.

Conclusion

The chapter Alternating Current is a crucial part of NEET Physics under electrodynamics and circuits. Mastery of RMS and peak values, reactance, impedance, resonance, power, and LC oscillations is essential for solving both conceptual and numerical problems.

StudentBro NEET Physics notes provide structured, clear, and exam-focused guidance, enabling aspirants to confidently solve AC questions and excel in NEET exams.