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Electricity and Magnetism

The Relation between Current, Charge and Time

Another analogy is often found to be helpful. Consider a pipe through which water is flowing. If the rate of flow of water through the pipe is, for example, 25min-1, then in 15minutes, the total quantity of water which has moved through the pipe is

The quantity of liquid is equal to the rate of flow multiplied by the time (in appropriate units).

Similarly, when considering a flow of electric charges, the quantity of charge which passes is given by

quantity of charge = rate of flow of charge × time

Q = I × t

As previously stated, the unit of charge is the Coulomb. The Coulomb can be now defined as follows:

1C is the quantity of charge which passes any point in a circuit in which a current of 1A flows for 1s

It should be noted that the Coulomb is a rather large quantity of charge. 1C is the quantity of charge carried by (approximately)

6×1018 electrons !!

 

© David Hoult 2008