The energy associated with electric field is $(U_E)$ and with magnetic field is $(U_B)$ for an electromagnetic wave in free space. Then

What happens to the intensity of light from a bulb if the distance from the bulb is doubled? As a laser beam travels across the length of a room, its intensity essentially remains constant. What geometrical characteristic of $LASER$ beam is responsible for the constant intensity which is missing in the case of light from the bulb ? 

In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of $2.0 \times 10^{10}\; Hz$ and amplitude $48\; Vm ^{-1}$

$(a)$ What is the wavelength of the wave?

$(b)$ What is the amplitude of the oscillating magnetic field?

$(c)$ Show that the average energy density of the $E$ field equals the average energy density of the $B$ field. $\left[c=3 \times 10^{8} \;m s ^{-1} .\right]$

Light wave traveling in air along $x$-direction is given by $E _{ y }=540 \sin \pi \times 10^{4}( x - ct ) Vm ^{-1}$. Then, the peak value of magnetic field of wave will be $\dots \times 10^{-7}\,T$ (Given $c =3 \times 10^{8}\,ms ^{-1}$ )

An EM wave from air enters a medium. The electric fields are $\overrightarrow {{E_1}}  = {E_{01}}\hat x\;cos\left[ {2\pi v\left( {\frac{z}{c} - t} \right)} \right]$ in air and $\overrightarrow {{E_2}}  = {E_{02}}\hat x\;cos\left[ {k\left( {2z - ct} \right)} \right]$ in medium, where the wave number $k$ and frequency $v$ refer to their values in air. The medium is nonmagnetic. If $\varepsilon {_{{r_1}}}$ and $\varepsilon {_{{r_2}}}$ refer to relative permittivities of air and medium respectively, which of the following options is correct?

An $EM$ wave propagating in $x$-direction has a wavelength of $8\,mm$. The electric field vibrating $y$ direction has maximum magnitude of $60\,Vm ^{-1}$. Choose the correct equations for electric and magnetic fields if the $EM$ wave is propagating in vacuum