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7. Alternating current — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics7. Alternating current1 Mark
MCQ
A coil has resistance $30\,ohm$ and inductive reactance $20\,ohm$ at $50\,Hz$ frequency. If an ac source, of $200\,volt$, $100\,Hz$, is connected across the coil, the current in the coil will be.......$A$
  • ✓
    $4$
  • B
    $8$
  • C
    $\frac {20}{\sqrt {13}}$
  • D
    $2$
✓

Answer

Correct option: A.
$4$
a
If $\omega=50 \times 2 \pi$ then $\omega L=20 \Omega$

If $\omega^{\prime}=100 \times 2 \pi$ then $\omega^{\prime} \mathrm{L}=40 \Omega$

Current flowing in the coil is

$I=\frac{200}{Z}=\frac{200}{\sqrt{R^{2}+\left(\omega^{\prime} L\right)^{2}}}=\frac{200}{\sqrt{(30)^{2}+(40)^{2}}}$

$I=4 A.$

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