Question

A magnet 10 m long and having a pole strength 2 amp m is deflected through ${30}^o$ from the magnetic meridian. The horizontal component of earth's induction is $0.32\times {10}^{-4}$ tesla then the value of deflecting couple is:

• A. $32\times {10}^{-7}Nm$
• B. $16\times {10}^{-7}Nm$
• C. $64\times {10}^{-7}Nm$
• D. $48\times {10}^{-7}Nm$

Answer 1

Answer: (A)

$32\times {10}^{-7}Nm$

$M=2\times \frac{10}{100}=0.2$
Value of restoring couple $=MHsin\varphi$

$=0.2\times 0.32\times {10}^{-4}sin{30}^o$
$=0.2\times 0.32\times {10}^{-4}\times \frac{1}{2}$

$=32\times {10}^{-7}Nm$