An electric bulb is rated as 200 ,W . What will be peak magnetic field ( × 10^{-8}, T ) at 4, m dis

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8.Electromagnetic waves

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An electric bulb is rated as $200 \,W$. What will be the peak magnetic field ($\times 10^{-8}\, T$) at $4\, m$ distance produced by the radiations coming from this bulb$?$ Consider this bulb as a point source with $3.5 \%$ efficiency.

A

$1.19$

B

$1.71$

C

$0.84$

D

$3.36$

(JEE MAIN-2022)

Solution

$\frac{\eta P }{4 \pi r ^{2}}=\frac{ cB _{0}^{2}}{2 \mu_{0}}$

$B _{0}=\sqrt{\frac{\mu_{0}}{4 \pi} \frac{\eta P }{ c } \frac{1}{ r }}$

$\Rightarrow B _{0}=\frac{1}{4} \sqrt{\frac{10^{-7} \times 4 \times 3.5}{3 \times 10^{8}}}=1.71 \times 10^{-8} \,T$

Standard 12

Physics

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