A laser beam can be focussed on an area equal to the square of its wavelength A $He-Ne$  laser radiates energy at the rate of $1\,mW$ and its wavelength is $632.8 \,nm$. The intensity of focussed beam will be

The electric field and magnetic field components of an electromagnetic wave going through vacuum is described by

$E _{ x }= E _0 \sin ( kz -\omega t )$

$B _{ y }= B _0 \sin ( kz -\omega t )$

Then the correct relation between $E_0$ and $B_0$ is given by

A plane electromagnetic wave of frequency $25\; \mathrm{GHz}$ is propagating in vacuum along the $z-$direction. At a particular point in space and time, the magnetic field is given by $\overrightarrow{\mathrm{B}}=5 \times 10^{-8} \hat{\mathrm{j}}\; \mathrm{T}$. The corresponding electric field $\overrightarrow{\mathrm{E}}$ is (speed of light  $\mathrm{c}=3 \times 10^{8}\; \mathrm{ms}^{-1})$

A plane electromagnetic wave of frequency $25 \;MHz$ travels in free space along the $x$ -direction. At a particular point in space and time, $E = 6.3\,\hat j\;\,V/m$. What is $B$ at this point? 

Select the correct statement from the following

Suppose that the electric field part of an electromagnetic wave in vacuum is

$E =\left\{(3.1 \;N / C ) \text { cos }\left[(1.8 \;rad / m ) y+\left(5.4 \times 10^{6} \;rad / s \right) t\right]\right\} \hat{ i }$

$(a)$ What is the direction of propagation?

$(b)$ What is the wavelength $\lambda$ ?

$(c)$ What is the frequency $v ?$

$(d)$ What is the amplitude of the magnetic field part of the wave?

$(e)$ Write an expression for the magnetic field part of the wave.