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JIPMER 2012
Exam
JIPMER
Year
2012
Subject
Physics
Chapter
Alternating Current

JIPMER 2012 · Physics · Alternating Current

An electric bulb has a rated power of 50 W at 100 V . If it is used...

An electric bulb has a rated power of 50 W at 100 V . If it is used on an AC source 200 V,50 Hz200 \mathrm{~V}, 50 \mathrm{~Hz}, a choke has to be used in series with it. This choke should have an inductance of

Options

  1. A0.1 mH
  2. B1 mH
  3. C0.1 H
  4. D1.1 H

Correct answer

D. 1.1 H

Step-by-step solution

Resistance of bulb R=V2P=(100)250R=\frac{V^2}{P}=\frac{(100)^2}{50} =200Ω=200 \Omega Current through bulb (I)=VR(I)=\frac{V}{R} =100200=0.5 A=\frac{100}{200}=0.5 \mathrm{~A} In a circuit containing inductive reactance (XL)\left(X_L\right) and resistance (R)(R), impedance (Z)(Z) of the circuit is Z=R2+ω2L2Z=\sqrt{R^2+\omega^2 L^2} ...(i) Here, Z=2000.5=400Ω\quad Z=\frac{200}{0.5}=400 \Omega Now, XL2=Z2−R2\quad X_L^2=Z^2-R^2 =(400)2−(200)2=(400)^2-(200)^2 (2πfL)2=12×104(2 \pi f L)^2=12 \times 10^4 L=23×1002π×50L=\frac{2 \sqrt{3} \times 100}{2 \pi \times 50} =23π=1.1H=\frac{2 \sqrt{3}}{\pi}=1.1 \mathrm{H}
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