Question
A rectangular coil of 100 turns has length 5cm and width 4cm. It is placed with its plane parallel to a uniform magnetic field and a current of 2A is sent through the coil. Find the magnitude of the magnetic field B if the torque acting on the coil is 0.2N m-1.

Answer

$\tau=\text{ni}\overrightarrow{\text{A}}\times\overrightarrow{\text{B}}$

$\Rightarrow\tau=\text{ni}\text{ AB}\sin90^\circ$

$\Rightarrow0.2=100\times2\times5\times4\times10^{-4}\times\text{B}$

$\Rightarrow\text{B}=\frac{0.2}{100\times2\times5\times4\times10^{-4}}=0.5$ Tesla

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