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11.Dual Nature of Radiation and matter
hard
A $2\,mW$ laser operates at a wavelength of $500\,nm.$ The number of photons that will be emitted per second is [Given Planck’s constant $h = 6.6 \times 10^{-34}\,Js,$ speed of light $c = 3.0\times 10^8\,m/s$ ]
A
$1\,\times 10^{16}$
B
$1.5\,\times 10^{16}$
C
$2\,\times 10^{16}$
D
$5\,\times 10^{15}$
(JEE MAIN-2019)
Solution
$2 \times {10^{ – 3}} = \frac{{{\text{hc}}}}{\lambda }\frac{{{\text{dn}}}}{{{\text{dt}}}}$
$\frac{{{\text{dn}}}}{{{\text{dt}}}} = \frac{{2 \times {{10}^{ – 3}}\lambda }}{{{\text{hc}}}}$
$ = \frac{{2 \times {{10}^{ – 3}} \times 500 \times {{10}^{ – 9}}}}{{6.6 \times {{10}^{ – 34}} \times 3 \times {{10}^8}}}$
$ = \frac{{1000}}{{6.6 \times 3}} \times {10^{14}}$ $ = 5 \times {10^{15}}$
Standard 12
Physics
