Question

Calculate the energy in Joules for a photon with a wavelength of 400 nm. Report your answer to 4 significant figures using scientific notation. (Ex: 1.345E-17 should be entered for 1.345 x 10^-17)

Answer 1

The energy (E) is found by multiplying Planck's constant (h) by the frequency (f).
That is: E = hf, where h is Planck's constant, equal to 6.625 * 10**-34 joule-sec.
The frequency is related to the wavelength (w) by: f = c/w, where c is the speed
of light, 2.9979 * 10**8 meters per second. Put these formulas together and we
obtain: E = hc/w
Since h and c are constant, their product hc is constant, 19.861 * 10**-26 J-m.
We are given w = 400 nanometers = 4.00 * 10**-7 meter.
So the energy E = hc/w = (19.861 * 10**-26 J-m) / (4.00 * 10**-7 m.)
E = 4.965 * 10**-19 joule to 4 significant figures