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6. Electromagnetic induction — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics6. Electromagnetic induction1 Mark
MCQ
Radius of a circular loop placed in a perpendicular uniform magnetic field is increasing at a constant rate of $r_0 ms ^{-1}$. If at any instant radius of the loop is $r$, then emf induced in the loop at that instant will be
  • A
    $-2 B r_0$
  • B
    $-2 B \pi r$
  • C
    $-B \pi r_0 r$
  • ✓
    $-2 B \pi r_0 r$
✓

Answer

Correct option: D.
$-2 B \pi r_0 r$
d
(d)

$\frac{d r}{d t}=r_0 \Rightarrow \phi=B \pi r^2$

$\varepsilon=\frac{-d \phi}{d t}=-B \pi(2 r) \frac{d r}{d t}$

$\varepsilon=-2 \pi B r r_0$

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