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8.Electromagnetic waves
hard
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
