Question

(1) Define electric current. What is the SI unit of electric current?
(2) Write the relation between a coulomb and an ampere?

Answer 1

Hint: For the first part recall the definition of electric current. When we say that there is current flowing in a circuit it is actually the charges that are moving. Also, SI unit of current was named after a physicist. Now you could recall which quantities have coulomb and ampere as their units and then find a relation between the two quantities and hence answer the second part.

Complete step by step answer:
(1) Electric current:
We could define electric current as the flow of charged particles like electrons or ions. We measure the current by calculating the time rate of flow of electric charge across a region. In general we call the moving particles that result in the production of electric current as charge carriers. These charge carriers can be anything depending on the conductor. We represent electric current conventionally by $I$. The expression for electric current $I$ is given by,
$I=\dfrac{q}{t}$
Where, q is charge flowing through the conductor and t is the time interval.
The SI unit of electric current is known to be ampere (A). Electric current can be measured using a device called ammeter.

(2) Relation between a coulomb and an ampere:
We know that coulomb is the SI unit of electric charge and ampere is the SI unit of current. From the definition of electric current we know that electric current is the time rate of change of electric charge. So, one ampere could be defined as the flow of one coulomb of electric charge in one second. That is,
$I=\dfrac{q}{t}$
$\therefore A=\dfrac{C}{s}$

Note:
Though the flow of negative charges determines the magnitude of current, it is also equal to flow of positive charges per unit time. But the conventional current is known to have the direction as that in which the positive charge flows. But as we know the direction of flow of negatively charged carriers is opposite to that.