Question

What is the energy (in electron volts - see More -Precisely 4-1 in the textbook) of a 470nm blue photon?

Express your answer using two significant figures.
E = __________ eV

Answer 1

The relationship between the energy of a photon (E) and the wavelength of the light (λ) is given by the formula, E = hc/λ
Where, h is Planck's constant and c is the speed of light.
h = 6.62 x 10^-34 Js and c = 3 x 10^8 m/sec
λ = 470 nm = 470 x 10^-9 m
Using all the values in the above formula,

E = (6.62 x 10^-34 x 3 x 10^8) / (470 x 10^-9)
E = (19.86 x 10^-26) / (470 x 10^-9)
E = (4.23 x 10^-19) Joule
E = 4.2 x 10^-19 Joule

1Joule = 6.24 x 10^18 eV
Therefore, 4.2 x 10^-19 Joule = 4.2 x 10^-19 x 6.24 x 10^18 eV
E = 2.6208 ~ 2.6 eV