If the radius of the potentiometer wire is doubled then effect on null point

CONCEPT:

Potentiometer:

• A potentiometer is a device mainly used to measure emf of a given cell and to compare emf’s of cells.
• It is also used to measure the internal resistance of a given cell.
• If V = E then no current will flow in the galvanometer circuit this condition to known as null deflection position, length l is known as balancing length.

In balanced condition E = kl or

\(E = \left( {\frac{e}{{R + {R_h} + r}}} \right)\frac{R}{L}l\)

Where R_h = Variable resistance which controls the current through the wire AB, E =emf of the cell, L = length of the potentiometer wire, l = balancing length and R = Resistance of potentiometer wire.

EXPLANATION:

• In the Balance condition emf of the battery is equal to the potential drop across potentiometer wire.
• From above it clear that emf of the battery depends on the resistance of the potentiometer wire.
• If the radius of the potentiometer wire is doubled, then the resistance of the potentiometer wire will decrease as resistance is inversely proportional to the area of the wire.
• The null point of a potentiometer depends on the ratio of the resistance of the two arms of the potentiometer wire.
• When the radius of the wire is doubled, the length and resistance per unit length of the wire remain the same.
• Therefore, the ratio of the resistance of the two arms of the potentiometer wire will remain the same, and the null point will remain unchanged.