**NEET Physics Notes Alternating Current-Power in an AC Circuit**

**Power in an AC Circuit**

**Power in an AC Circuit**

Let a voltage be applied across an AC and consequently a current flows through the circuit. Then,

**Instantaneous power = VI**

**Average power over a full cycle of AC is**

**Wattless Current**

Average power is given by The phase difference between E rms and I rms is Φ We can resolve lrms into two components

Here, the component contributes towards power dissipation and the component does not contribute towards power dissipation. Therefore, it is called Wattless current.

**L-C Oscillations**

An L-C circuit also called a resonant circuit, tank circuit or tuned circuit consists of an inductor and a capacitor when connected together they can act as an electrical resonator, storing energy oscillating at the circuits resonant frequency.

The energy oscillates back and forth between the capacitor and inductor until internal resistance makes the oscillations die out. The oscillation frequency is determined by the capacitance and inductance values.

**Choke Coil**

Let us consider a choke coil (used in tube lights) of large inductance L and low resistance R. The power factor for such a coil is given by

the current passing through the coil is very small. Such a coil is used in AC circuits for the purpose of adjusting current to any required value without waste of energy. The only loss of energy is due to hystersis in the iron core, which is much less than the loss of energy in the resistance that can also reduce the current, if placed instead of the choke coil.