**Sinusoidal Current**

A sinusoidal alternating current is represented by;

I = I_{0} sinωt where I_{0 }is the peak value

The current varies like a sine wave so it is called sinusoidal.

**Alternating Voltage**

The magnitude of the power dissipated in a resistor is given by the expression:

I^{2}R or VI or V^{2}/R

The current and voltage is represented by;

I = I_{0 }sinωt

V = V_{0} sinωt

And the peak value is I_{0 }and V_{0}.

The power generated in the resistance R is given by the usual Formula

P = I^{2}R

But current I must be written as;

I = I_{0} sinωt

So,

P = I^{2}R sin^{2}ωt

Since I_{0} and R are constant so;

= ½ V_{0}^{2}/R = ½ I_{0}^{2}R

**Root mean squared values**

Average value of the square of current or voltage is given as;

<I^{2}> = ½ I_{0}^{2}

<V^{2}> = ½ V_{0}^{2}

SO,

The root mean square value of alternating current is that steady current which delivers the same average power as the a.c. to resistive load.

**Transformers**

A transformer is a device used to change the voltage of a circuit using electromagnetic induction. It consists of a soft iron core wrapped on both side with wire. The first coil of wire is called primary coil and the other coil is secondary coil.

A current flows through the primary coil which creates magnetic field which cuts through the turns of wire on the secondary coil. This induces the e.m.f. and current in second coil.

**Transformers type:**

- Step Up transformer

Where V_{s}> V_{p} or N_{s} > N_{p}

- Step down transformer

Where V_{p} > V_{s} or N_{s} < N_{p}

**In both cases **

**N _{S}/N_{P} = V_{S}/V_{P} = I_{P}/I_{S}**

**Rectification**

It is the process of converting alternating current a.c. into direct current d.c.

Full wave rectification involves four diodes and is referred to as a bridge rectifier circuit. Diodes are used to convert a.c. to d.c. A single diode gives half-wave rectification. A bridge of four diodes gives full-wave rectification. A capacitor soothes the rectified voltage.