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13. Current Electricity eLearn.Punjab
If a net charge 3Q passes through any cross section of a conductor in time 3t, we say that an
electric current I has been established through the conductor where
∆ Q
I = .....(13.1)
t ∆
The SI unit of current is ampere and it is a current due to flow of charge at the rate of one coulomb
per second.
Motion of electric charge which causes an electric current is due to the flow of charge carriers. In
case of metallic conductors, the charge carriers are electrons. The charge carriers in electrolyte are
−−
positive and negative ions e.g. in a CuSO solution the charge carriers are Cu and SO ions. In
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gases, the charge carriers are electrons and ions.
Current Direction
Early scientists regarded an electric current as a flow of positive
Interesting information
charge from positive to negative terminal of the battery through
an external circuit. Later on, it was found that a current in metallic
conductors is actually due to the flow of negative charge carriers
called electrons moving in the opposite direction i.e. from
negative to positive terminal of the battery, but it is a convention
to take the direction of current as the direction in which positive
charges flow. This current is referred as conventional current. It
has been found experimentally that positive charge moving in one
direction is equivalent in all external effects to a negative charge
When eel senses danger, it turns itself
into a living battery. Any one who moving in the opposite direction. As the current is measured
attacks this fish is likely to get a shock. by its external effects so a current due to motion of negative
The potential difference between the
head and tail of an electric eel can be charges, after reversing its direction of flow can be substituted
upto 600 V. by an equivalent current due to flow of positive charges. Thus
The conventional current in a circuit is defined as that equivalent current
which passes from a point at higher potential to a point at a lower
potential as if it represented a movement of positive charges.
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