Question

What is the wavelength of a 2.0-eV red photon?

Express your answer to two significant figures and include the appropriate units.

Answer 1

E = (h x c) / λ
2.0 eV = (6.626 x 10^-34 J.s) x (3 x 10^8 m/s) / λ
2.0 x (1.6 x 10^-19) J = 1.9878 x 10^-25 / λ
(3.2 x 10^-19) x λ = 1.9878 x 10^-25
λ = 6.211875 x 10^-7
(1 nm = 10^-9 m)
λ = 620 nm