Question

A cell of negligible internal resistance is connected to a tangent galvanometer and the deflection produced is ${30}^o$. If three such cells are connected in series and the combination is connected to the same galvanometer, the deflection will be

• A. ${30}^o$
• B. ${60}^o$
• C. ${90}^o$
• D. ${45}^o$

Answer 1

Answer: (B)

${60}^o$

$I=K\tan \theta$
where I is the current and $\theta$ is the angle by which the compass needle rotates.
When the three cells are connected in series, the current will be three times.
$\therefore \frac{I_1}{3I_1}=\frac{\tan {30}^{\circ }}{\tan \theta }$
$\Rightarrow \tan \theta =\sqrt{3}$
$\Rightarrow \theta ={60}^{\circ }$