State Joule's law of heating.

Read the following statements carefully and state whether each statement is true or false:
$(i)$ The quantity of charge flowing past a point multiplied by time is current.
$(ii)$ The flow of charge through a conducting wire connected to a cell is the result of a chemical reaction inside the cell.
$(iii)$ The resistivity of all pure metals increases with an increase in temperature.
$(iv)$ Ohm's law is a relation between the power used in a circuit to the current and the potential difference.
$(v)$ $A$ series circuit has only one conducting path for the electrons that move through it; a parallel circuit has multiple conducting paths.
$(vi)$ $A$ conducting wire offers resistance to the flow of electrons because electrons repel each other in the wire.

Explain the terms potential and potential difference. Give their $SI$ units.

If the resistance of a conductor is doubled,the current is halved.

An electric oven hot plate is connected to a $200 \, V$ line. It has two resistance coils $A$ and $B$,each of $30 \, \Omega$,which may be used separately,in series,or in parallel. Find the value of the current required in each of the three cases.

The unit of electric potential difference is $.....$