Electric Current and Circuit

Electric current is defined as the rate of flow of charges across any cross sectional area of a conductor. Thus current I is expressed in units as ampere. The direction of conventional current is taken as the direction of flow of positive charges or opposite to the direction of flow of electrons. If a net charge Q, flows across any cross-section of a conductor in time t, then the current through the cross-section is

Where Q is in coulomb and t is in seconds. The current I is expressed in the unit ampere. The magnitude of the charge of the electron is 1.610-19 C (Coulomb)

Question

How to define one ampere?

Solution
One ampere is constituted by the flow of one coulomb of charge per second, .

Milliampere (1mA = 10-3 A) or Microampere (1Î¼ A = 10-6A) Both are used to measure the small quantity of current.

The electric circuit demonstrated by the combination of battery, light bulb and wires consists of two distinct parts: the internal circuit and the external circuit. The part of the circuit containing the battery is the internal circuit. The part of the circuit where charge is moving outside the battery through the wires and the light bulb is the external circuit. The electric current flows in the circuit from the positive terminal of the cell to the negative terminal of the cell through the bulb and ammeter.