A UV lamp used for water purification operates at a power of $6.6 \text{ W}$ and emits monochromatic light of wavelength $300 \text{ nm}$ . How many photons are emitted by the lamp per second?
(Take $h = 6.6 \times 10^{-34} \text{ J s}$ and $c = 3 \times 10^8 \text{ m/s}$ )

Question

A UV lamp used for water purification operates at a power of

6.6 \text{ W}

and emits monochromatic light of wavelength

300 \text{ nm}

. How many photons are emitted by the lamp per second?
(Take

h = 6.6 \times 10^{-34} \text{ J s}

and

c = 3 \times 10^8 \text{ m/s}

)

Quantrex Academy · Accepted Answer

Correct answer: B. 10^ 19

Energy of a single photon is given by E = (hc)/(λ) Substituting the given values: E = 6.6 × 10^ -34 × 3 × 10^8 300 × 10^ -9 E = 19.8 × 10^ -26 3 × 10^ -7 = 6.6 × 10^ -19 J Let n be the number of photons emitted per second. The total power P is given by P = nE n = (P)/(E) = 6.6 6.6 × 10^ -19 n = 10^ 19 Answer: 10^ 19

A UV lamp used for water purification operates at a power of 6.6 W...

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