Question

What is the photon flux and photon density at 2 m from the lamp?

• A. $5.9\times {10}^{14}photonsc{m}^{-2},2\times {10}^{4}photonsc{m}^{-2}$
• B. $2\times {10}^{4}photonsc{m}^{-2},5.9\times {10}^{14}photonsc{m}^{-2}$
• C. $5.9\times {10}^{10}photonsc{m}^{-2},2\times {10}^{3}photonsc{m}^{-2}$
• D. $2\times {10}^{3}photonsc{m}^{-2},5.9\times {10}^{10}photonsc{m}^{-2}$

Answer 1

The correct option is A $5.9\times {10}^{14}photonsc{m}^{-2},2\times {10}^{4}photonsc{m}^{-2}$

$P=100W,\lambda =5890A^0$

Intensity, $I=\frac{P}{A}=\frac{100}{4\pi r^2}=\frac{100}{4\times \pi \times 4}=1.98W/㎡also,I=\frac{nhc}{\lambda 4\pi r^{2}t}\therefore photonflux=\frac{n}{4\pi r^{2}t}=\frac{I\times \lambda }{hc}=\frac{1.98\times 5890\times {10}^{-10}}{6.6\times {10}^{-34}\times 3\times {10}^8}=5.91\times {10}^{18}\times {10}^{-4}=5.91\times {10}^{14}photon/㎠$