Calculating the frequency of light from wavelength for visible light Photosystem

Question

Calculating the frequency of light from wavelength for visible light

Photosystem I absorbs photons of red light having a wavelength of 700 nm. This leads to excitation of one electron at the "reaction center" into an excited state. We want to calculate how much energy one mole of these electrons in this excited state have above the ground state, in kJ/mole, so we can compare to ATP (50 kJ/mole), covalent bonds, thermal energy, etc. This energy allows the electron to be transferred, eventually to form NADPH.

First we need to know how to calculate the frequency from the wavelength, using the right equation. This problem generates random frequencies in the visible range (400 - 800 nm) for you to practice on: What is the frequency of photons having wavelength 793 nm? Note: This is a big number because visible light frequencies are high! I'm afraid you will have to put the extra zeros in your answer because Canvas doesn't always take scientific notation.

Hint: Be sure to convert wavelength in nanometers (nm) to meters!

Explanation / Answer

Energy = hC/wave legnth

and frequency = C/wave length, C = speed of light = 3*108m/sec and Wave length= 793 nm= 793*10-9m

Frequency= 3*108/793*10-9=3.783*1014/sec

from E= h* frequency, h= plancks constant = 6.627*10-34 j.s

Energy of single photon = 3.783*1014* 6.627*10-34 J=2.51*10-19 J

energy of 1 mole of photons = 6.023*1023* 2.51*10-19 Joules =151000 Joules = 151Kj/mole

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