The electric field intensity

Question:

The electric field intensity produced by the radiation coming from a $100 \mathrm{~W}$ bulb at a distance of $3 \mathrm{~m}$ is E. The electric field intensity produced by the radiation coming from $60 \mathrm{~W}$

at the same distance is $\sqrt{\frac{\mathrm{x}}{5}} \mathrm{E}$. Where the value of $x=$

Solution:

$\mathrm{c} \in_{0} \mathrm{E}^{2}=\frac{100}{4 \pi \times 3^{2}}$

$c \in_{0}\left(\sqrt{\frac{\mathrm{x}}{5}} \mathrm{E}\right)^{2}=\frac{60}{4 \pi \times 3^{2}}$

$\Rightarrow \frac{x}{5}=\frac{3}{5}$

$\Rightarrow x=3$