Question

Write the principle on which the working of a metre bridge is based. In an experiment on meter bridge, student obtains the balance point at the point $J$ such that $AJ=40cm$, as shown in figure. The values of $R$ and $X$ are both doubled and then interchanged. Find the new position of the balance point. If the galvanometer and battery are also interchanged how will the position of balance point be affected

Answer 1

Wheatstone bridge works the the principle of a balanced meter bridge which is satisfied of the wheatstone condition that is when the variable resistor is adjusted, then the current in the galvanometer becomes zero, the ratio of two two unknown resistors is equal to the ratio of value of unknown resistance and adjusted value of variable resistance. By using a Wheatstone Bridge the unknown electrical resistance value can easily measure. When the values of both X and R are doubled and then interchanged, the balance point still remained the same. So the resistance X is:

$$\begin{array}{c}\frac{R}{X}=\frac{40}{100-40}=\frac{40}{60}\\ X=\frac{3}{2}R\end{array}$$

Since the condition of the bridge is still satisfied there will be no deflection in the galvanometer.