Question 14 Marks

How do we express electric current? Electric current is defined by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges. In circuits using metallic wires, electrons constitute the flow of charges. However, electrons were not known at the time when the phenomenon of electricity was first observed. So, electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current. Conventionally, in an electric circuit, the direction of electric current is taken as opposite to the direction of theflow of electrons, which are negative charges.

i. If a net charge Q , flows across any cross-section of a conductor in time $\mathbf{t}$, then the current $\mathbf{I}$, through the cross-section is given by which formula?
ii. What is the SI unit of electric charge? It is equivalent to how many numbers of electrons?
iii. The electric current is expressed in which unit? Define the unit used to measure electric current.
OR
If the amount of charge passing through the cell in 4 seconds is 12 C then find the current supplied by a cell.

Answer

i. If a net charge Q , flows across any cross-section of a conductor in time ' t ', then the current ' I ', through the cross-section isgiven by $\mathrm{I}=\frac{Q}{T}$
ii. The SI unit of electric charge is the coulomb (C), which is equivalent to the charge contained in nearly $6 \times 10^{18}$ electrons.
iii. The electric current is expressed by a unit called ampere (A). One ampere is constituted by the flow of one coulomb of chargeper second.
OR
$I=\frac{Q}{t}=\frac{12}{4}=3 A$

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