Wheatstone Bridge and Potentiometer

Wheatstone Bridge

An electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component.

Potentiometer

A device used for measuring or comparing potential differences, EMFs, and internal resistance of cells without drawing any current from the source.

Balance Condition (Wheatstone Bridge)

The state of a Wheatstone Bridge where no current flows through the galvanometer, indicating that the potential difference across its terminals is zero.

Potential Gradient

The potential drop per unit length along a conductor, typically a uniform wire in a potentiometer, when a constant current flows through it.

Wheatstone Bridge Balance Condition

Applicable when the galvanometer current is zero (bridge is balanced).

P/Q = R/S

Metre Bridge Formula for Unknown Resistance

S is known resistance, l1 is balance length from the end where R_unknown is connected.

R_unknown = S * (l1 / (100 - l1))

Potentiometer Principle (Potential Drop)

V is potential drop, k is potential gradient (V/L), l is length.

V = k * l

Comparison of EMFs using Potentiometer

l1 and l2 are balance lengths for cells with EMFs E1 and E2 respectively.

E1/E2 = l1/l2

Internal Resistance of a Cell using Potentiometer

R is external resistance, E is cell EMF (balance length l1), V is terminal potential difference (balance length l2) when current flows through R.

r = R * ((E/V) - 1) = R * ((l1/l2) - 1)