Question

If there is no deflection in the galvanometer connected in a circuit shown in figure, then the ratio of lengths $AC/CB$ is

• A. $4:1$
• B. $1:4$
• C. $1:1$
• D. $2:1$

Answer 1

The correct option is A $4:1$

We know that,
Resistance of wire $\propto$ Length of wire

$\therefore \frac{R_{AC}}{R_{CB}}=\frac{AC}{CB}$

The galvanometer will show zero deflection in the balanced condition of bridge.

Thus,

$\frac{60\Omega }{15\Omega }=\frac{R_{AC}}{R_{CB}}=\frac{AC}{CB}$

$\frac{AC}{CB}=\frac{4}{1}=4:1$

Therefore, option $\left(a\right)$ is correct.

Why this question ? Tip: In problems involving meter bridge, the resistance of the portion of meter bridge wire will be proportional to its length.