Some Definitions Regarding Alternating Voltage and Current

When a coil rotates in a magnetic field, it produces alternating voltage and current. These values reach their maximum in two positions of the coil. This maximum value is called the peak value or amplitude.

The time taken by the alternating current to complete one cycle is called the periodic time, denoted by T.

The number of cycles completed by an alternating current in one second is called the frequency of the current.

T = \[\frac {2π}{ω​}\]

• f = \[\frac {1}{T}\]

Since T = \[\frac {2π}{ω}\]​: f = \[\frac {ω}{2π}\]

Unit: Cycles per second (c/s) or Hertz (Hz)

• For voltage: V₀
• For current: I₀

Think of the coil rotating — at two specific positions during rotation, the voltage or current produced is at its highest. That highest value is the peak value.

In one complete rotation of a coil rotating in a magnetic field:

1. Current rises from zero to maximum in one direction
2. Falls from maximum to zero
3. Rises from zero to maximum in the opposite direction
4. Falls back to zero

This complete sequence is called one cycle of current.

Physical Meaning: Frequency equals the number of rotations completed by the coil in 1 second.

Domestic AC in India: The frequency of domestic alternating current is 50 cycles/second or 50 Hz.

Key Relationship: Frequency and periodic time are inverses of each other:

• If you know T, find f using f = \[\frac {1}{T}\]
• If you know f, find T using T = \[\frac {1}{f}\]