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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Thermal and Chemical Effects of Electric Current

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Thermal and Chemical Effects of Electric Current

A bulb with a rating of 250 V , 100 W is connected to a 220 V power...

A bulb with a rating of 250 V250 \text{ V}, 100 W100 \text{ W} is connected to a 220 V220 \text{ V} power supply situated 10 m10 \text{ m} away, utilizing a copper wire with a cross-sectional area of 5 mm25 \text{ mm}^2. Determine the power consumed by the connecting wires. The resistivity of copper is 1.7×10−8Ωm1.7 \times 10^{-8} \Omega \text{m}.

Options

  1. A0.014 W0.014 \text{ W}
  2. B0.011 W0.011 \text{ W}
  3. C0.0084 W0.0084 \text{ W}
  4. D0.0042 W0.0042 \text{ W}

Correct answer

C. 0.0084 W0.0084 \text{ W}

Step-by-step solution

The resistance of the bulb is given by:

R=V2P=2502100=625ΩR = \dfrac{V^2}{P} = \dfrac{250^2}{100} = 625 \Omega

Since the power supply is situated 10 m10 \text{ m} away, a complete circuit requires both a forward and a return path. Thus, the total length of the connecting wire is:

l=2×10=20 ml = 2 \times 10 = 20 \text{ m}

The resistance of the connecting wire is:

Rw=ρlA=1.7×10−8×205×10−6=0.068ΩR_w = \rho \dfrac{l}{A} = \dfrac{1.7 \times 10^{-8} \times 20}{5 \times 10^{-6}} = 0.068 \Omega

The total resistance of the circuit is:

Req=R+Rw=625+0.068≈625ΩR_{\text{eq}} = R + R_w = 625 + 0.068 \approx 625 \Omega

The current flowing through the circuit is:

I=V′Req=220625=0.352 AI = \dfrac{V'}{R_{\text{eq}}} = \dfrac{220}{625} = 0.352 \text{ A}

The power consumed by the connecting wires is:

Pw=I2Rw=(0.352)2×0.068≈0.1239×0.068≈0.0084 WP_w = I^2 R_w = (0.352)^2 \times 0.068 \approx 0.1239 \times 0.068 \approx 0.0084 \text{ W}
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