Question

A tangent galvanometer has $80$ turns of wire. The internal and external diameters of the coil are $19cm$ and $21cm$ respectively. The reduction factor of the galvanometer at a place where $H=0.32$ oersted will be ($1$ oersted $=80A/m$)

• A. $0.0064$
• B. $0.64$
• C. $0.064$
• D. $Noneofthese$

Answer 1

The correct option is C $0.064$

$\begin{array}{c}reductionfactor,k=\frac{2R{B}_H}{N{\mu }_o}\\ R=\frac{r_1+r_2}{2}=\frac{\frac{19}{2}+\frac{21}{2}}{2}=\frac{40}{4}=10\\ B_H={\mu }_{o}H\\ k=\frac{2\times 10\times {\mu }_o\left(0.32\times 80\right)}{80\times {\mu }_o\times 100}\\ =\frac{0.32\times 20}{100}=\frac{0.64}{10}=0.064\end{array}$