The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is:

$\frac{E}{\sqrt{2}}$

We know that, We know that, $E_0 \propto \sqrt{P_{av}}$

∴  $\frac{\left(E_0\right)_1}{\left(E_0\right)_2}=\sqrt{\frac{\left(P_{av}\right)_1}{\left(P_{av}\right)_2}}$

$\Rightarrow \frac{E}{\left(E_0\right)_2}=\sqrt{\frac{100}{50}}$

$\left(E_0\right)_2=\frac{E}{\sqrt{2}}$