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Physics · 2025 · 2 marks
Dual Nature of Radiation and MatterParticle Nature of Light: The Photon2 marksApplyvery short answer
CBSE 2025 · Region 6 · Set 1 · Q19
A laser beam of frequency 3.0 × 10^14 Hz produces average power of 9 mW. Find (i) the energy of photon of the beam, and (ii) the number of photons…
A laser beam of frequency $\displaystyle 3.0 \times 10^{14} \mathrm{~Hz}$ produces average power of $\displaystyle 9$ mW.
Find
(i)
the energy of photon of the beam, and
(ii)
the number of photons emitted per second on an average by the source.
Marking-scheme solution
Finding-
(i)
\(\displaystyle \mathrm{E}=\mathrm{h} v\)
\[\begin{aligned}
& =6.63 \times 10^{-34} \times 3.0 \times 10^{14} \\
& =1.99 \times 10^{-19} \mathrm{~J}
\end{aligned}
\]
(ii)
\(\displaystyle N=\frac{P}{\mathrm{E}}\)
\[\begin{aligned}
& =\frac{9 \times 10^{-3}}{1.99 \times 10^{-19}} \\
& =4.5 \times 10^{16}
\end{aligned}
\]
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