Exam-style question
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What is the energy of a photon with a wavelength of 400 nm?.
- A.4.97 x 10^-19 J
- B.5.00 x 10^-19 J
- C.4.96 x 10^-19 J
- D.4.90 x 10^-19 J
Model answer
What a good answer should say
- 4.97 x 10^-19 J
Explanation
Why this works
To find the energy of a photon, we use E = hf. First, convert wavelength to frequency using c = fλ, where c = 3 x 10^8 m/s and λ = 400 nm = 400 x 10^-9 m.
Thus, f = c/λ = (3 x 10^8 m/s) / (400 x 10^-9 m) = 7.5 x 10^14 Hz. Now, E = hf = (6.63 x 10^-34 J·s)(7.5 x 10^14 Hz) = 4.97 x 10^-19 J.
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