# A moving coil galvanometer has a coil with $175$ turns and area   $1\:\:cm^{2}$. It uses a torsion band of torsion constant $10^{-6}\:\:N-m/rad$ . The coil is placed in a magnetic field B parallel to its plane . The coil deflects by  $1^{0}$ for a current of $1\:\:mA$ . The value of B ( in Tesla ) is approximately : Option 1) $10^{-4}$ Option 2) $10^{-2}$ Option 3) $10^{-1}$ Option 4) $10^{-3}$

Given

$N=175$

$A=1\:\:cm^{2}$

$\Phi =\frac{\pi}{180}\:rad$

$I=10^{-3}A$

$C=10^{-6}N-m$

$\Rightarrow BINA=C\Phi$

$B=\frac{C\Phi}{INA}$

$B=\frac{10^{-6}}{10^{-3}\times 175 \times 10^{-4}}\times \frac{\pi}{180}=0.0010$

$B=10^{-3}\:\:Tesla$

Option 1)

$10^{-4}$

Option 2)

$10^{-2}$

Option 3)

$10^{-1}$

Option 4)

$10^{-3}$

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