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  • An electric bulb is rated as 200 W. What will be the peak magnetic field at 4 m distance produced by the radiations coming from this bulb? Consider this bulb as a point source with 3.5% efficiency.

An electric bulb is rated as 200 W. What will be the peak magnetic field at 4 m distance produced by the radiations coming from this bulb? Consider this bulb as a point source with 3.5% efficiency.

Option: 1

1.19 \times 10^{-8}T


Option: 2

1.71 \times 10^{-8}T


Option: 3

0.84 \times 10^{-8}T


Option: 4

3.36 \times 10^{-8}T


Answers (1)

best_answer

Power emitted from source =\mathrm{3.5 \%} of \mathrm{200 \mathrm{~W}} 
\mathrm{ \begin{aligned} &=\frac{3.5}{100} \times 200 \\ P_{0} &=7 w \end{aligned} }
Intensity at pt. A

\mathrm{ A=I=\frac{1}{2} \frac{B_{0}^{2}}{\mu_{0}} C }

                 \mathrm{ \frac{P_{0}}{4 \pi r^{2}}=\frac{1}{2} \frac{B_{0}^{2}}{\mu_{0}} C}
\begin{array}{r} \because \mu_{0}=4 \pi \times 10^{-7} \\ \\ \frac{7}{16}=\frac{B_{0}^{2} \times 3 \times 10^{8}}{2 \times 10^{-7}} \\ \\ B_{0}^{2}=\frac{14}{48} \times 10^{-15} \\ \\ B_{0}^{2}=\frac{140}{48} \times 10^{-16} \\ \\ \Rightarrow \quad B_{0}=1.71 \times 10^{-8} \mathrm{~T} \end{array}

The correct option is (2)

Posted by

Shailly goel

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