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Magnetic Field — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsMagnetic Field2 Marks
Question
A rectangular coil of $100$ turns has length $5\ cm$ and width $4\ cm$. 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 $0.2\ N m^{-1}.$
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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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