The layer of the atmosphere that reflects low frequency $(LF)$ electromagnetic waves during day time only is

If the amplitude of the magnetic field in a travelling plane electromagnetic wave is $2.2 \times 10^{-4} \ T$,then the intensity of the wave is nearly

Given below are two statements: one is labelled as Assertion $(A)$ and other is labelled as Reason $(R).$
Assertion $(A):$ Electromagnetic waves carry energy but not momentum.
Reason $(R):$ Mass of a photon is zero.
In the light of the above statements,choose the most appropriate answer from the options given below:

The electric field for an electromagnetic wave in free space is $E = i 30 \cos (k z - 5 \times 10^8 t)$,where the magnitude of $E$ is in $V/m$. The magnitude of the wave vector $k$ is (velocity of electromagnetic wave in free space $= 3 \times 10^8 \ m/s$).

$A$ magnetic field vector in an electromagnetic wave is represented by $\vec{B} = B_0 \sin(2\pi vt - \frac{2\pi x}{\lambda}) \hat{j}$. Its associated electric field vector is . . . . . . .

The ratio of the speeds of electromagnetic waves in a vacuum and in a medium with dielectric constant $K=3$ and permeability $\mu=2\mu_{0}$ is (where $\mu_{0}$ is the permeability of vacuum).