$(a)$ What is an electric circuit?
$(b)$ Calculate the number of electrons that flow per second to constitute a current of one ampere. The charge on an electron is $1.6 \times 10^{-19} \ C$.
$(c)$ Draw an electric circuit for studying Ohm's law. Label the circuit components used to measure electric current and potential difference.

(N/A) An electric circuit is a continuous and closed path in which an electric current can flow.
$(b)$ We know that $I = Q / t$ and $Q = n e$,where $n$ is the number of electrons and $e$ is the charge on an electron. Therefore,we have:
$I = n e / t$
$n = (I \times t) / e = (1 \ \text{A} \times 1 \ \text{s}) / (1.6 \times 10^{-19} \ \text{C})$
$n = 6.25 \times 10^{18}$ electrons.
$(c)$ The circuit diagram used to study Ohm's law is shown below.
Electric current is measured by an Ammeter $(A)$.
Potential difference is measured by a Voltmeter $(V)$.