If $\overrightarrow E $ and $\overrightarrow B $ are the electric and magnetic field vectors of E.M. waves then the direction of propagation of E.M. wave is along the direction of

The speed of electromagnetic wave in a medium (whose dielectric constant is $2.25$ and relative permeability is $4$ ) is equal to .......... $\times 10^8 \,m / s$

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

A plane electromagnetic wave travels in vacuum along $z-$ direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is $30 \;MHz$, what is its wavelength in $m$?

The energy of electromagnetic wave in vacuum is given by the relation

Two electrons are moving with same speed $v$. One electron enters a region of uniform electric field while the other enters a region of uniform magnetic field. Then after some time if the de-broglie wavelength of the two are ${\lambda _1}$ and ${\lambda _2}$  then