In the previous article, we have learned about Maxwell bridge. It is a modification of Maxwell’s bridge. The circuit diagram for Hay’s Bridge is shown below. It uses a resistance in series with a standard capacitor.

L_{1}=unknown resistance having a resistance R_{1}

R_{2}, R_{3}, R_{4}=known non-inductive resistance

C_{4}=standard capacitor

At balance,

e_{1}e_{4} = e_{2}e_{3}

Separating real and imaginary term from above equation, we get

By solving the above two equations, we get

The Q factor of the coil is given by

## Advantages

1) provides very simple expression for unknown inductance for high Q coils. This bridge is suitable for coils having Q > 10.

2) simple expression for Q factor.

3) From the expression of Q-factor, it is clear that for high Q factor the value of resistance R_{4} should be small.

## Disadvantages

1) This bridge is suitable for measurement of high Q inductors.