Direct current and alternate current

There are two types of electric current : direct current (DC) and alternate current (AC).

Magnitude and direction of DC are constant, while those of AC are varying.

EMF occurs from AC, not from DC.

Electricity from outlet (socket) is AC, and thus it occurs EMF.

On the other hand, battery-operated devices such as a clock does not occur EMF since electricity of batteries is DC.

So, why is AC applied to electricity from outlet (socket)?

It’s because electric power transmission of AC is technically easier than that of DC.

Electricity with quite high voltage (from 275,000 up to 500,000V) is generated at power plants for minimizing electrical loss during transmission.

Such electricity is gradually stepped down its voltage at substations, and finally reaches to homes after decreased to 100V or 200V by transformers on power poles.

Nowadays DC power transmission is partly launched for testing, but seems to be required more time until it becomes commercial realities.