Meter bridge

Theory

A Wheatstone bridge finds an unknown resistance by comparing ratios. When the bridge balances, the galvanometer’s terminals have the same potential and no current flows through it. In a meter bridge, a uniform 100 cm wire forms the two adjustable ratio arms.

Place X in the left gap and R in the right gap. If l is the balance length measured from the left end, X/R = l/(100 − l). The relation assumes a uniform wire with negligible resistance at contacts and ends. Swap the two resistances and compare results to look for systematic error.

X/R = l/(100 − l)

Measure l in cm from the left end, with X in the left gap. X and R are resistances in Ω.