$(i)$ Name and state the law that gives the relationship between the current through a conductor and the potential difference across its two terminals. Also,express this law mathematically.
$(ii)$ Draw the $V-I$ graph for this law. Justify your answer.
$(iii)$ Write the name and use of the circuit components whose symbols are given below:
$(a)$ $A$ resistor with an arrow through it.
$(b)$ $A$ circle with a dot inside,connected to two lines.

(N/A) $(i)$ Ohm's law.
It states that,provided the physical conditions remain the same,the current flowing through a conductor is directly proportional to the potential difference across its two ends.
Mathematically,we have $V \propto I$ or $V = IR$,where $R$ is the resistance of the conductor.
$(ii)$ The $V-I$ graph is a straight line passing through the origin. This justifies the law because a straight-line graph indicates that the potential difference $V$ is directly proportional to the current $I$ $(V \propto I)$.
$(iii)$ $(a)$ Variable resistor (Rheostat): It is used to vary the resistance in the circuit to control the current.
$(b)$ Closed switch (or closed key): It allows the current to flow through the circuit by completing the path.