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 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
$1.5 \times {10^{13}}\,W/{m^2}$
- B
$2.5 \times {10^9}\,W/{m^2}$
- C
$3.5 \times {10^{17}}\,W/{m^2}$
- D
None of these
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The electric field associated with an $e.m.$ wave in vacuum is given by $\vec E = \hat i\,40\,\cos \,\left( {kz - 6 \times {{10}^8}\,t} \right)$. where $E$, $z$ and $t$ are in $volt/m$, meter and seconds respectively. The value of wave factor $k$ is ....... $m^{-1}$.
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There exists a uniform magnetic and electric field of magnitude $1\, T$ and $1\, V/m$ respectively along positive $y-$ axis. A charged particle of mass $1\,kg$ and of charge $1\, C$ is having velocity $1\, m/sec$ along $x-$ axis and is at origin at $t = 0.$ Then the co-ordinates of particle at time $\pi$ seconds will be :-
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