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Current:

When two bodies (or conductors) are rubbed together, they get charged due to friction with charges

equal in magnitude, but of opposite kinds. A positively charged body has a deficient of electrons, while a

negatively charged body has an excess of electrons. The charges can be made to flow between them by

suitable arrangements. For example, if two charged bodies are joined by a metallic wire, electrons flowfrom the body having more electrons to the body having fewer electrons. The flow of electrons (i.e., a

charge in motion) constitutes an electric current. The rate of flow of charge gives the magnitude of

electric current.

The rate of flow of electrons is called electronic current in that direction. The conventional current or

simply current is in a direction opposite to the direction of motion of electrons.

Potential Difference or voltage:

We know that like charges repel and unlike charges attract, therefore to create an excess or deficient of

electrons at a point, some work is to be done in moving the charges( or electrons) against the force

between them. Hence quantitatively, the potential difference is measured in terms of the work done in

transferring the charge from one conductor to the other through the metallic wire. We define potential

difference as follows:

The current in a conductor is the rate of flow of charge across the cross-section of

that conductor, the cross-section being normal to the direction of flow of current.

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If W work is done in transferring a test charge q from one conductor to the other, the potential

difference between them is

V=

Power:

By the definition of potential difference, the work W done in moving a charge Q across the ends ofconductor.

Power is the rate of doing work. Since work and energy are considered to be equivalent, so in an

electrical circuit, we define power as the rate at which electrical energy is supplied by the source.

OR

BY Ohms law, V=IR

P=I2R

Also by ohms law, I=

Thus, electrical Power

UNITS OF POWER : The SI units of power are Watts(W) or J S-1

.

The potential difference between two conductors is equal to the work done

in transferring a unit positive charge from one conductor to the other

conductor through the metallic wire.

P=

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For Example: If the power of an electrical appliance is one watt-hour. It implies that the electrical

energy spent by an electrical appliance of power one watt when it is used for 1 hour.(1 watt is the rating

of appliance).

1 watt-hour=1 watt * 1 hour

= 1W *(60*60s)=3600J

Thus, 1Wh=3600J

IIIly

, one kilowatt-hour(or KWh) is the electrical energy consumed by an electrical appliance of power

1Kw when it is used for 1 hour.

1 kilowatt-hour(1 KWh) = 1 kilowatt * 1 hour

=1000 watt * 1 hour

=1000 Js-1

* (60 * 60 s)

=3.6*106

J

Thus,

1KWh=3.6 * 106

J