$A$ point source of electromagnetic radiation has an average power output of $800 \ W$. Find the maximum value of the magnetic field at a distance of $3.5 \ m$ from the source.

The electron density of $E, F_1,$ and $F_2$ layers of the ionosphere is $4 \times 10^{11} \, m^{-3}, 9 \times 10^{11} \, m^{-3},$ and $16 \times 10^{11} \, m^{-3}$ respectively. What is the ratio of the critical frequencies for the reflection of radio waves?

Given below are two statements:
Statement $I$: $A$ time-varying electric field is a source of a changing magnetic field and vice-versa. Thus,a disturbance in an electric or magnetic field creates $EM$ waves.
Statement $II$: In a material medium,the $EM$ wave travels with speed $v = \frac{1}{\sqrt{\mu_{0} \varepsilon_{0}}}$.
In the light of the above statements,choose the correct answer from the options given below:

The electric field in $NC^{-1}$ of an electromagnetic wave is given by $E = 36 \sqrt{\pi} \sin(\omega t - kx)$. The average energy density of the electromagnetic wave due to the electric field is (Given: $\frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \ Nm^2 C^{-2}$)

About $5 \%$ of the power of a $100 \; W$ light bulb is converted to visible radiation. What is the average intensity of visible radiation
$(a)$ at a distance of $1 \; m$ from the bulb?
$(b)$ at a distance of $10 \; m$? Assume that the radiation is emitted isotropically and neglect reflection.

The electromagnetic waves do not transport