Question

The electric and magnetic fields produced by the radiation coming from a 100 W bulb at a distance of 3m is respectively [Assume that the efficiency of the bulb is $2.5\%$ and it is a point source]

• A. $2.9V/mand9.6\times {10}^{-8}T$
• B. $2.9V/mand9.6\times {10}^{-9}T$
• C. $29V/mand4.8\times {10}^{-9}T$
• D. $5.8V/mand4.8\times {10}^{-9}T$

Answer 1

The correct option is B $2.9V/mand9.6\times {10}^{-9}T$

$I=\frac{P}{4\pi r^2}\Rightarrow I=\frac{100}{\left(4\pi \right)(3{)}^2}\times \frac{2.5}{100}=0.022W/m^2{I}_E=\frac{1}{2}=0.011W/m^2{I}_E=\frac{1}{2}={\epsilon }_0{E}^{2}C\Rightarrow E=\sqrt{\frac{2I_E}{{\epsilon }_{0}C}}=2.9V/m$
Now, $B=\frac{E}{C}=\frac{2.9}{3\times {10}^8}=9.6\times {10}^{-9}T$