JEE Mains · Physics · STD 12 - 8. Electromagnetic waves
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 \(3.36\)
Answer & Solution
Correct Answer
(B) \(1.71\)
Step-by-step Solution
Detailed explanation
\(\frac{\eta P }{4 \pi r ^{2}}=\frac{ cB _{0}^{2}}{2 \mu_{0}}\) \(B _{0}=\sqrt{\frac{\mu_{0}}{4 \pi} \frac{\eta P }{ c } \frac{1}{ r }}\) \(\Rightarrow B _{0}=\frac{1}{4} \sqrt{\frac{10^{-7} \times 4 \times 3.5}{3 \times 10^{8}}}=1.71 \times 10^{-8} \,T\)
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