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6. Electromagnetic induction — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics6. Electromagnetic induction1 Mark
MCQ
A certain elastic conducting material is stretched into a circular loop. It is placed with its plane perpendicular to a uniform magnetic field $B =0.8\,T$. When released the radius of the loop starts shrinking at a constant rate of $2\,cm ^{-1}$. The induced emf in the loop at an instant when the radius of the loop is $10\,cm$ will be $........mV$.
  • ✓
    $10$
  • B
    $11$
  • C
    $12$
  • D
    $13$
✓

Answer

Correct option: A.
$10$
a
$EMF =\frac{ d }{ dt }\left( B \pi r ^2\right)$

$=2 B \pi r \frac{ dr }{ dt }=2 \times \pi \times 0.1 \times 0.8 \times 2 \times 10^{-2}$ $=2 \pi \times 1.6= 1 0 . 0 6 \text { [round off } 1 0 . 0 6 = 1 0 ]$

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