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11.Dual Nature of Radiation and matter
medium
A $160 \,W$ light source is radiating light of wavelength $6200 \,\mathring A$ uniformly in all directions. The photon flux at a distance of $1.8 \,m$ is of the order of .......... $m ^{-2} s ^{-1}$ (Planck's constant $\left.=6.63 \times 10^{-34} \,J - s \right)$
A
$10^2$
B
$10^{12}$
C
$10^{19}$
D
$10^{25}$
(KVPY-2014)
Solution
(c)
Photon flux $=$ Number of photons per unit area per unit time
$=\frac{I}{\left(\frac{h c}{\lambda}\right)}=\frac{I \lambda}{h c}=\frac{P \lambda}{4 \pi r^2 h c}$
$=\frac{160 \times 6200 \times 10^{-10}}{4 \times \pi \times(1.8)^2 \times 6.63 \times 10^{-34} \times 3 \times 10^8}$
$=1.22 \times 10^{19} \,m ^{-2} s ^{-1}$
Standard 12
Physics
