Electric bulb draws a current of $0.4\ ampere$. Calculate the amount of charge flowing through the bulb if the bulb glows for two hours also calculate the number of electrons passed.

Given:

Current, $I$ = 0.4 A

Time, $t$ = 2 hours = $2\times {3600}$ = 7200 sec   (time is converted into seconds)

To find: Electric charge, $(Q)$ flowing through the bulb.

Solution:

We know that, 

$Q=I\times {t}$

where, $Q$ = Charge in coulombs (C), $I$ = Current in amperes (A), $t$ = time in seconds (s).

Substituting the given values in the formula, we get-

$Q=0.4\times {7200}$

$Q=\frac {4}{10}\times {7200}$

$Q={4}\times {7200}$

$Q=2880C$

Thus, the charge flowing through the bulb in two hours is 2880C.

Now, we know that-

$Q=N\times {e}$

where, $N$ = No. of electrons, $Q$ = Total charge and $e$ = Electronic charge on an electron $(1.6\times {10^{-19}})$C.

Substituting the value of $Q$ and $e$ we get-

$Q=N\times {e}$

$2880=N\times {1.6\times {10^{-19}}}$

$N=\frac {2880}{1.6\times {10^{-19}}}$

$N=\frac {2880\times {10^{19}}}{1.6}$

$N=\frac {2880\times {10^{20}}}{16}$

$N=180\times {10^{20}}$

$N=1.8\times {10^{22}}$

Thus, the number of electrons passed is $1.8\times {10^{22}}$.

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Updated on: 10-Oct-2022

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