Concepts to remember on the “Capacitive Circuits- Alternating Currents” for JEE and CBSE board exams:

Capacitors and Capacitance:

• Capacitance: The ability of a capacitor to store electrical charge. Measured in farads (F).
• Capacitors in AC circuits: Capacitors oppose the changes in voltage and allow the flow of alternating current.
• Charging and discharging of capacitors in AC circuits: Capacitors charge and discharge alternately during each cycle of AC.

Reactance and Impedance:

• Inductive reactance (XL): Opposition to the flow of AC due to inductance. Measured in ohms.
• Capacitive reactance (XC): Opposition to the flow of AC due to capacitance. Measured in ohms.
• Impedance (Z): Combination of resistance (R), inductive reactance (XL), and capacitive reactance (XC). Measured in ohms.
• Phase difference: Difference in the timing between voltage and current waveforms in AC circuits.

Power and Power Factor:

• Average power: The amount of power delivered or consumed in an AC circuit over a complete cycle. Measured in watts (W).
• Reactive power: The power that flows back and forth between the source and the circuit, not contributing to actual work. Measured in volt-amperes reactive (VAR).
• Power factor (PF): The ratio of average power to apparent power (combination of average power and reactive power). Ranges from 0 to 1.
• Power factor correction methods: Techniques to improve the power factor, such as using capacitors or synchronous condensers.

Resonant Circuits:

• Resonance: Condition when the inductive reactance (XL) and capacitive reactance (XC) cancel each other out, resulting in maximum current flow.
• Resonant frequency (f_r): The frequency at which resonance occurs.
• Series resonant circuit: A circuit with inductance (L) and capacitance (C) connected in series.
• Parallel resonant circuit: A circuit with inductance (L) and capacitance (C) connected in parallel.
• Quality factor (Q-factor): Measure of the sharpness of resonance, indicating the energy storage capacity of the circuit.

AC Generators and Transformers:

• AC generators: Convert mechanical energy into electrical energy by rotating a coil in a magnetic field.
• Emf equation: E = Blv, where E is the emf generated, B is the magnetic field strength, l is the length of the conductor, and v is the velocity of the conductor.
• Frequency: Number of cycles per second in an AC waveform. Measured in hertz (Hz).
• Transformers: Transfer electrical energy from one circuit to another through electromagnetic induction.
• Turns ratio: Ratio of the number of turns in the primary coil to the number of turns in the secondary coil.
• Voltage and current transformation: Voltage and current in the secondary coil are directly proportional to the turns ratio.