Electric Current
The flow of charge in a definite direction constitutes the electric current and the time rate of flow of charge through any cross-section of a conductor is the measure of current
Electric current = total charge flowing / time taken = q/t
Consider both the positive and negative charges be flowing forward and backward normally across a small area in a time interval t let q + be the net amount (forward minus backward) or positive charge that flows in the forward direction across the given area and let q – be the net amount of negative charge that flows in the forward direction across that area. The net amount of charge flowing across the given area in the forward direction in time t is
Q = q + - q-
Electric current
I = net charge flowing / time taken = q / t
If the value of q is positive then the direction of current is forward. In equation (1) if the value of q comes out to be – ve then the direction of current is backward.
Sometimes the charges flowing normally through and area may boot be steady but varying with time then we can define the current as follows. Let ?Q be the net amount of positive charge flowing normally across a crossest one of the conductor in direct on in a time interval t and t + ?t. then at time t the current in the conductor is given by
I = lim ? t -> ?Q / ?t = dQ / dt
Where dQ/dt is the first derivative of Q w.r.t. it means current through a conductor at a time is defined as the first derivative of charge with respect to time passing through a cross- section of the conductor in a particular direction.
Unit of electric current
S.I unit of current is ampere. It is also called practical unit of current,. It is denoted by A where
1 ampere (A) = 1 coulomb / 1 second = 1 Cs–1
Thus the current through a wire is said to be I ampere, if one coulomb of charge is flowing per second through a section of the wire.
Direction of electric current as a matter of convention the direction of flow of positive charge gives the direction of current. This is called conventional current. The direct on of flow of electrons gives the direction of electronic current the direction of electronic current is opposite to that of conventional current in as end A is connected to positive terminal of cell, the conventional current is flowing through the conductor from A to B. the direction of electronic current will be from B to A.
Through a cross-section of the conductor in a time t, if the total positive charge is flowing from A to B and total negative charge q2 is flowing from B to A then total current through the conductor is
I = q1 / t + q2 / t
Its direction is from A to B
2. The average lightning carries currents of the order of tens of thousands of amperes.
3. The currents in our nerves are in microamperes.
Current is a scalar quantity. Thought the electric current represents the direction of flow of positive charge, het it is treated as a scalar quantity because for its addition, the laws of scalar addition are applicable and not the laws of vector addition the angle between the wires carrying currents does not affect the total current in the circuit.
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