A source S1 is producing, 1015 photons per second of wavelength 5000 A. Another source S2 is producing 1.02 × 1015 photons per second of wavelength 5100 A. Then, (power of S2)/(power of S1) is equal to (a) 1.00 (b) 1.02 (c) 1.04 (d) 0.98

Answer: (a). Power P = n(hc)/(λ) ⇒ P ∝ (n)/(λ). (P₂)/(P₁) = (n₂)/(n₁) · (λ₁)/(λ₂) = 1.02 × (5000)/(5100) (P₂)/(P₁) = (1.02)/(1.02) = 1.00 So the answer is (a) 1.00.

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Photons: Energy, Momentum & Radiation Pressure

A source S1 is producing, 1015 photons per second of wavelength 5000 $\mathring{A}$ . Another source S2 is producing 1.02 $\times$ 1015 photons per second of wavelength 5100 $\mathring{A}$ . Then, (power of S2)/(power of S1) is equal to

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Answer: (a)

Power $P = n\frac{hc}{\lambda} \Rightarrow P \propto \frac{n}{\lambda}$ .
$\frac{P_2}{P_1} = \frac{n_2}{n_1} \cdot \frac{\lambda_1}{\lambda_2} = 1.02 \times \frac{5000}{5100}$
$\frac{P_2}{P_1} = \frac{1.02}{1.02} = 1.00$
So the answer is (a) 1.00.

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