Maxwell bridge is used to measure
Right Answer is:
A Maxwell bridge is a modification to a Wheatstone bridge used to measure an unknown inductance (usually of low Q value) in terms of calibrated resistance and inductance or resistance and capacitance.
As in the balanced condition of the Wheatstone bridge product of opposite arms, resistance is equal i.e
R1R3 = R2R4
In Maxwell AC bridge in the two arms, there are two pure resistances so that for balance relations, the phase balance depends on the remaining two arms.
For the balanced condition of the Maxwell AC bridge
Z1Z3 = Z2Z4
Where Z1 is the unknown Impedance
Z1 = R1 + JX1 = R1 + JωL1
Z4 is the know Impedance
Z4 = R4 + JX4 = R4 + JωL4
R2 and R3 = Known pure resistance
∴ (R1 + JωL1)R3 = (R4 + JωL4)R2
Equating real and Imaginary part
R1R3 = R2R4
ωL1R3 = ωL4R2
L1R3 = L4R2
Hence, the unknown self-inductance can be measured in terms of the known inductance L4 and the two resistors. Resistive and reactive terms balance independently and the conditions are independent of frequency. This bridge is often used for measuring the iron losses of the transformers at audio frequency.