Question

The torque of an ammeter varies as the square of the current through it. If a current of 10 A produces a deflection of ${90}^o$. The deflection for a current of 5 A when the instrument is gravity controlled, is _______degrees.

• A. 20
• B. 14.5
• C. 30
• D. 10

Answer 1

The correct option is B 14.5

$T_e\propto sin\theta$
$sin\theta \propto I^2$

$or,\frac{sin{\theta }_2}{sin{\theta }_1}={\left(\frac{I_2}{I_1}\right)}^2$

$or,{\theta }_2=si{n}^{-1}\left[{\left(\frac{I_2}{I_1}\right)}^{2}sin{\theta }_1\right]$

$=si{n}^{-1}[{\left(\frac{5}{10}\right)}^2\times 1]=si{n}^{-1}0.25={14.5}^o$