What is the main principle involved in a Voltaic cell?

$(a)$ In the circuit shown, connect a nichrome wire of length $L$ between points $X$ and $Y$ and note the ammeter reading.
$(i)$ When this experiment is repeated by inserting another nichrome wire of the same thickness but twice the length $(2L)$, what changes are observed in the ammeter reading?
$(ii)$ State the changes that are observed in the ammeter reading if we double the area of cross-section without changing the length in the above experiment. Justify your answer in both cases.
$(b)$ "Potential difference between points $A$ and $B$ in an electric field is $1\, V$." Explain the statement.

An electric bulb works on the heating effect of current.

$A$ piece of wire of resistance $6 \, \Omega$ is connected to a battery of $12 \, V$. Find the amount of current flowing through it. Now,the same wire is redrawn by stretching it to double its length. Find the resistance of the new (redrawn) wire.

Three resistors $R_{1} = 5 \Omega$,$R_{2} = 10 \Omega$,and $R_{3} = 30 \Omega$ are connected in parallel to a $12 \; V$ battery. Which resistor will have the highest current flowing through it?

What is electrical resistivity? In a series electrical circuit comprising a resistor made up of a metallic wire, the ammeter reads $5\, A$. The reading of the ammeter decreases to half when the length of the wire is doubled. Why?