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Magnetism — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsMagnetism1 Mark
Question
Assertion : When radius of circular loop carrying current is doubled, its magnetic moment becomes four times.
Reason $\quad$ : Magnetic moment depends on area of the loop.
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Answer

(b) Magnetic dipole moment of the current loop$=\text { Ampere turns } \times \text { Area of the coil }$Initially magnetic moment $M=i \pi r$, new magnetic moment $M^{\prime}=i \pi(2 r)^2=4 i\left(\pi r^2\right)=4 M$

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