Question

In a potentiometer of ten wires, the balance point is obtained on the sixth wire. To shift the balance point to eighth wire, we should
A) Increase resistance in the primary circuit.
B) Decrease resistance in primary circuit.
C) Decrease resistance in series with the cell whose e.m.f has to be measured.
D) Increase resistance in series with the cell whose e.m.f has to be measured.

Answer 1

We will be using ohm’s law equation which states that the potential difference across the conductor is directly proportional to current passing through it.
${\text{V = IR}}$ [I=current and R=resistance]
I is inversely proportional to R

Important Formulae
${\text{V = IR}}$

Complete step by step solution
When resistance in the main circuit is increased the current through the wire due to decreases as we know from the equation ${\text{V = IR}}$, we can identify that I is inversely proportional to R and so the potential difference of the wire decreases therefore it requires more length to measure the e.m.f of secondary cell.
So, therefore by increasing the resistance in the series circuit we can move the balancing point from sixth to eight wire. So, the potential drop, which earlier existed on the 6th wire, may now be found on the 8th wire.

Thus option A is correct.

Additional information
The resistance of a conductor is measured in Ohms and the Ohm is a unit named after the German physicist George Simon Ohm (1787-1854) who was the first to show the relationship between resistance, current and voltage.

Note: An electric circuit is formed when a current path is created inside a conductor to allow electric charge to move continuously. This continuous movement of electric charge through the conductors of a circuit is called a current.