The electric field of a plane electromagnetic wave propagating through a non-magnetic medium is given by $E = 20 \cos (2 \times 10^{10} t - 200 x) \, V/m$. The dielectric constant of the medium is equal to: (Take $\mu_r = 1$)

In fog, photographs of the objects taken with infrared radiations are more clear than those obtained during visible light because

In a plane electromagnetic wave travelling in free space,the electric field component oscillates sinusoidally at a frequency of $2.0 \times 10^{10} \text{ Hz}$ and amplitude $48 \text{ V m}^{-1}$. Then the amplitude of the oscillating magnetic field is: (Speed of light in free space $= 3 \times 10^8 \text{ m s}^{-1}$)

In an electromagnetic wave,the amplitude of the electric field is $1 \ V/m$. The frequency of the wave is $5 \times 10^{14} \ Hz$. The wave is propagating along the $z$-axis. The average energy density of the electric field,in $J/m^3$,will be:

An electromagnetic wave of wavelength $2 \times 10^{-10} \,m$ passes from vacuum into a dielectric medium of relative permittivity $4$. Then its wavelength will be

$A$ radio can tune in to any station in the $7.5\; MHz$ to $12\; MHz$ band. What is the corresponding wavelength band?