$A$ radar sends an electromagnetic signal with an electric field $E_{0} = 2.25\,V/m$ and a magnetic field $B_{0} = 1.5 \times 10^{-8}\,T$,which strikes a target on the line of sight at a distance of $3\,km$ in a medium. After that,a part of the signal (echo) reflects back towards the radar with the same velocity and along the same path. If the signal was transmitted at time $t_{0}$ from the radar,then after how much time (in $\times 10^{-5}\,s$) will the echo reach the radar?

$A$ physical quantity $\vec{S}$ is defined as $\vec{S}=(\vec{E} \times \vec{B}) / \mu_0$,where $\vec{E}$ is the electric field,$\vec{B}$ is the magnetic field,and $\mu_0$ is the permeability of free space. The dimensions of $\vec{S}$ are the same as the dimensions of which of the following quantity(ies)?
$(A)$ $\frac{\text{Energy}}{\text{charge} \times \text{current}}$
$(B)$ $\frac{\text{Force}}{\text{Length} \times \text{Time}}$
$(C)$ $\frac{\text{Energy}}{\text{Volume}}$
$(D)$ $\frac{\text{Power}}{\text{Area}}$

The electromagnetic flux from the Sun reaching the Earth is $10^3 \ W m^{-2}$. What is the power incident on a roof of dimensions $6 \ m \times 30 \ m$?

For a $GPS$ navigation to track a mobile device,we use :-

Assertion : Microwaves are better carrier of signals than optical waves.
Reason : Microwaves move faster than optical waves.

$A$ laser beam is operating at $100 \,mW$. The amount of energy stored by $90 \,cm$ length of this laser beam will be