UP Board - Class 12 physics - Chapter 7: Alternating Current Handwritten Notes

Alternating current (AC) is the type of electric current that periodically reverses direction, unlike direct current (DC), which flows in only one direction. AC is commonly used in power supply systems and for operating household appliances and industrial machinery.

Key Points:

1. Characteristics of AC:

   • In AC, the direction of current flow changes periodically.
   • The voltage and current alternate in a sinusoidal manner.
   • AC frequency is typically measured in hertz (Hz), and common frequencies are 50 Hz or 60 Hz depending on the country.

2. Peak and RMS Values:

   • The peak value is the maximum value of the current or voltage in the cycle.
   • The RMS (Root Mean Square) value is the effective value of AC, representing the equivalent DC value that would produce the same heating effect.

3. Power in AC Circuits:

   • Power in AC circuits depends on the voltage and current variations over time.
   • The average power is determined by the phase difference between voltage and current. In purely resistive circuits, the voltage and current are in phase, leading to efficient power transfer.

4. Impedance and Reactance:

   • Impedance is the total opposition to current flow in AC circuits, combining both resistance and reactance.
   • Reactance is the opposition to current caused by inductors or capacitors in the circuit.

5. Resonance in AC Circuits:

   • Resonance occurs when inductive reactance and capacitive reactance cancel each other out, resulting in maximum current flow.

6. Transformer:

   • A transformer uses AC to change voltage levels, either stepping it up or stepping it down. This is important for power transmission across long distances.

7. Applications of AC:

   • AC is widely used for powering homes, industries, and appliances like lights, fans, and air conditioners.
   • It is also essential in electric motors and many electronic devices.
     

Conclusion:

Alternating current is crucial for the operation of modern electrical systems. Its ability to alternate direction and be easily transformed for different voltage levels makes it ideal for energy distribution. AC is an essential component of everyday life, from household appliances to industrial machinery and large-scale power systems.

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