Question

In an electric bulb, a current of 10A flows for 2hrs. Find the amount of charge that has passed through the bulb.
A. 36000C
B. 720C
C. 72000C
D. 3600C

Answer 1

Hint: Current is the amount of charge flowing through a conductor in a unit time. The current in a conductor is given by $i=\dfrac{q}{t}$, where ‘i’ is the current, q is the total charge flown in a given time and t is that given time.

Complete step-by-step answer:
Electric bulb acts as a resistance through which the current (i) flows. Current is the rate of charge flowing through a conductor with respect to time. It tells us the amount of charges is flowing in one unit of time. It is given by $i=\dfrac{q}{t}$ ……(1), where q is the total charge flown in a given time and t is that given time. The SI unit of current is ampere (A) and the SI unit of charge is column. 1 ampere current means that 1 column of charge is flowing in the wire in one second of time. We can rewrite equation (1) as $q=it$ . Now, we calculate the charge flown through the bulb in 2 hours of time. Here, i=10A and $t=2hr=2\times 60\min =2\times 60\times 60\sec =7200\sec $
Therefore, $q=it=10\times 7200=72000C$. Which means that a total charge of 72000C passed through the bulb in 2 hours.
Hence, the correct option is (c) 72000C.

Note: $i=\dfrac{q}{t}$ , is true only for a uniform constant current. The rate of charge flowing does change with time or we can also say that for the amount of charge flowing each second is same/constant. When the current is varying with time, we consider the instantaneous current i.e. current at a particular instant time. It is given by $i=\dfrac{dq}{dt}$. dt is a very small (almost equal to zero) interval time in which dq amount charge flows.