Use the balance length

A metre bridge has unknown resistance X in its left gap and 6 Ω in its right gap. The balance point is 40 cm from the left end of the uniform 100 cm wire.

Find X.

Organize the givens & assumptions

right resistance = 6 Ω
left wire length = 40 cm
right wire length = 60 cm

Uniform bridge wire; ideal null detector; negligible lead, contact and end resistances; steady DC.

A $2.4\ \Omega$
B $6\ \Omega$
C $4\ \Omega$
D $9\ \Omega$

Try it on paper first. Free sample problems in every collection include the complete reasoning: find one in this collection →