Question

The bridge circuit shown in the figure below is used for the measurement of an unknown element $Z_x$. The bridge circuit is best suited when $Z_x$ is a

• A. low resistance
• B. high resistance
• C. low Q inductor
• D. lossy capacitor

Answer 1

The correct option is C low Q inductor

The bridge is Maxwell bridge.

Element is an inductor.

$\text{Inductance=}{L}_x\text{effective resistance of the inductor =}{R}_x$

$Q=\frac{\omega L_x}{R_x}=\omega C_1{R}_1$

The bridge is limited to measurement of low Q inductor (1<Q<10).

It is clear from equation (i) that the measurement of high Q coils demands a large value of resistance $R_1$, perhaps ${10}^{5}or{10}^6\Omega$. The resistance boxes of such high values are very expensive. Thus for values of Q>10, the bridge is unsuitable.

The bridge is also unsuited for coils with a very low values of Q(i.e. Q<1).