What is the different between single phase & three phase

This comes up periodically.

Can you tell me why you need to know? For what application?

Curious.

3 phase is used for higher power requirement, single phase no, just low power. 3 phase comes at you in 3 pulses, each lagging the other by degrees. and is wired different than 1 phase, in what's called a star-delta or a wye configure. I have seen reduced-voltage Magnetic Starters with mechanical interlocks and overload relay heaters gr because a motor is a inductive load an if it goes into locked rotor condition you neerd the overloads to trip and shut down the circuit before trouble. With heating or lighting loads, which is resistive, not inductive, you do not need a overload, no. There would be no lock rotor potential like in a inductive motor load so that's the difference right there.

3 phase can be a smaller motor than 1 phase.

Three phases are used to sort of 'simulate' DC.
Why not use DC in the first place?
Because it is difficult/expensive to step DC up or down.
Why step it up/down?
Because the higher the voltage, the lower the current. The lower the current the lower the losses. If you want to 'transport' or transmit electricity over longer distances, then you need high voltages to keep the losses down. It's technically easy to step up voltages (using a transformer).
Regards,
Chris

The difference between single phase and three phase is that the single phase is just an alternating waveform of about 110 or 120 volt where as two phase are the two alternating waves that are 180 degree apart from each other i.e. when one of the signal is +ve the other signal is -ve and vice versa thus giving us the continuous power where as three phase contains three signals that are 120 degree apart from each other thus giving the continuous power

Phase means the differnce between the waves, through which the current flows. 1 phase consists of 3 wires , 1 phase 1 neutral and 1 stay wire. 3 phase consists of 5 wires , 3 phases(R, Y, B), 1 neutral and 1 stay wire. In most of the transformers 3 phases are mostly used except the road side transformers because the voltage of 3 phase is 440v. In domestic appliances 1 phase is used because the voltage required is 230v.