The refractive index of the ionosphere is

$A$ cube of unit volume contains $35 \times 10^7$ photons of frequency $10^{15} \text{ Hz}$. If the energy of all the photons is viewed as the average energy being contained in the electromagnetic waves within the same volume,then the amplitude of the magnetic field is $\alpha \times 10^{-9} \text{ T}$. Taking permeability of free space $\mu_0 = 4\pi \times 10^{-7} \text{ Tm/A}$,Planck's constant $h = 6 \times 10^{-34} \text{ Js}$ and $\pi = \frac{22}{7}$,the value of $\alpha$ is $.....$

An electromagnetic wave travels along the $z$-axis. Which of the following pairs of space and time-varying fields would generate such a wave?

What are called non-mechanical waves? Give its examples.

In an electromagnetic wave,the phase difference between the electric and magnetic field vectors $\vec{E}$ and $\vec{B}$ is:

If a plane electromagnetic wave has electric field oscillations of frequency $3 \text{ GHz}$, then the wavelength of the wave is (speed of light in vacuum $= 3 \times 10^8 \text{ m/s}$) (in $\text{ m}$)