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## Thursday, March 11, 2010

### what is an electric current?

As we have seen in an earlier post, an electric current will only flow if their is a complete circuit. You have also seen that an electric current is also due to the flow of electrons.

Fig 1 below show a complete circuit. As you can see from the circuit electrons will flow through the bulb on its way to the positive terminal of the power supply.

Fig 1

Now depending on the circuit a certain number of electrons will flow through the bulb every second.

Hence if we know the number of electrons that is flowing through the bulb every second, then it means that we cal calculate the amount of charge that flow through the bulb in one second.

Example 1

If the number of electrons that flows through the bulb in 10 s is 3.0x1022 and the charge of one electron is 1.6 x 10-19 C,

Calculate (i) the amount of charge that flows through the bulb in 10 s.

(ii) the amount of charge that flows through the bulb in 1 s.

Ans

(i) The amount of charge flowing though the bulb in 10 s is

Q = 3.0 x 1022 *1.6x10-19

= 4800 C

(ii) The amount of charge flowing through the bulb in 1s is

Q = 4800/10 =480 C

Now the quantity electric current is defined as the rate of flow of electric charge.

The unit of electric current is the Ampere (A) .

Thus if we are able to determine the rate of flow of electric charge or the amount of charge that flows in a circuit element like the bulb every second it means that we have determined the electric current.

If the amount of charge  flowing through the bulb every second is 480 C then

The electric current = 480 C /s or 480 A.

Thus we can conclude that the electric current is merely an indication of the amount of charge flowing per second in a circuit element.  The more charge flowing per second the greater the electric current flowing through the circuit element.