Question

The magnetic needle of a tangent galvanometer is deflected at an angle ${30}^o$ due to a magnet. The horizontal component of earth's magnetic field $0.34\times {10}^{-4}T$ is along the plane of the coil. The magnetic intensity (of coil) is

• A. $1.96\times {10}^{-4}T$
• B. $1.96\times {10}^{5}T$
• C. $1.96\times {10}^{-5}T$
• D. $1.96\times {10}^{4}T$

Answer 1

The correct option is C $1.96\times {10}^{-5}T$

In a tangent galvanometer, the magnetic field of coil and horizontal field earth are mutually perpendicular


Coil's magnetic field,

$B=B_{H}tan\theta$

Where, $B_H$ is horizontal component of magnetic field and $\theta$ is angle of deflection respectively and the magnetic needle is deflected along the resultant field which is at angle $\theta$ with $B_H$

$\therefore B=0.34\times {10}^{-4}tan{30}^o$

$B=1.96\times {10}^{-5}T$

Hence, the correct option is (B)