Alternating Current
Complete Alternating Current roadmap for RMS value, phasor diagrams, reactance, impedance, LCR resonance, power factor, transformers and exam-oriented practice.physics notes/alternating current
Average and RMS Value of AC Waveform
Understand average value, RMS value, peak value, peak-to-peak value, form factor and effective value of AC waveforms.
AC Circuits with Resistor, Inductor and Capacitor
Study pure resistor, pure inductor, pure capacitor, reactance, impedance and phase relation in AC circuits.
AC Circuits with RL and RC Combination
Learn RL circuit, RC circuit, impedance, phase angle, phasor diagrams and numerical applications.
LCR Circuit, Resonance and Power in AC Circuit
Understand series LCR circuit, resonance, resonant frequency, power factor, wattless current and quality factor.
Transformer
Learn the principle, construction, working, step-up transformer, step-down transformer and transformer losses.
Alternating Current Important Questions
Practice NCERT questions, CBSE board questions, NEET MCQs, JEE Main questions and JEE Advanced problems.
Need Help in Alternating Current?
Alternating Current is an important chapter for CBSE, NEET, IIT JEE Main and IIT JEE Advanced. If you are facing difficulty in RMS value, phasor diagrams, AC circuits, LCR resonance, power factor or transformers, you can directly learn from Kumar Sir through one-to-one Physics classes.
AC Basics and Phasor Diagram
Alternating current and alternating voltage vary sinusoidally with time. In AC circuits, the magnitude changes continuously and the direction reverses periodically. Phasor diagrams help us compare voltage and current by using phase angle.
1. AC Waveform Basics
In a sinusoidal AC waveform, instantaneous voltage and current are written as functions of time. The peak value, RMS value and average value are different quantities and must not be confused.
v = V₀ sin(ωt)i = I₀ sin(ωt)Vpp = 2V₀- v is the instantaneous value of voltage.
- V₀ is the peak value or amplitude of voltage.
- 2V₀ is the peak-to-peak value of voltage.
- Vrms is the root mean square value of voltage.
- Vavg is the average value of voltage.
- RMS value represents the effective AC value.
- Average value represents the DC component present in the waveform.
2. Same Phase Case
Equations: v = V₀ sin(ωt), i = I₀ sin(ωt)
3. Current Lagging Case
Equations: v = V₀ sin(ωt), i = I₀ sin(ωt − φ)
4. Current Leading Case
Equations: v = V₀ sin(ωt), i = I₀ sin(ωt + φ)
5. Difference Between AC and DC
| Feature | AC | DC |
|---|---|---|
| Direction | Direction changes periodically. | Direction remains constant. |
| Magnitude | Magnitude changes with time. | Magnitude usually remains constant. |
| Transformation | Can be stepped up or stepped down easily using transformer. | Cannot be stepped up or stepped down easily without electronic converters. |
| Uses | Used in homes and power transmission. | Used in batteries, mobile phones, electronics and DC motors. |
| Common Supply | India: about 230 V, 50 Hz. USA: about 120 V, 60 Hz. | Battery supply such as 1.5 V, 3.7 V, 12 V etc. |
6. Why AC is Used in Homes
- AC voltage can be transformed easily using transformers.
- High-voltage transmission reduces power loss in long-distance lines.
- AC generation and distribution are economical on large scale.
- Most household supply systems use AC because the grid is designed for AC distribution.
- In India, domestic AC supply is approximately 230 V and 50 Hz.
- In the USA, domestic AC supply is approximately 120 V and 60 Hz.
7. Three Phase AC System
RYB system means Red, Yellow and Blue phases. The three phases are separated by 120 degrees. In a balanced three-phase system, the resultant of the three phase currents is zero. This makes three-phase supply very useful for power distribution and heavy electrical machines.
Need Help in Alternating Current?
If you are facing difficulty in AC waveform, RMS value, average value, phasor diagram, AC circuits, resonance, power factor or transformer, you can learn personally from Kumar Sir through one-to-one Physics classes.