Question

Blue light and ultraviolet light are both shown upon a surface of sodium and cause the ejection of electrons. Which light will cause the ejected electrons to have a higher kinetic energy

Answer 1

ultraviolet light (UV) has more energy than blue light, so electrons must have higher kinetic energy

Step-by-step explanation:

This is a photoelectric effect exercise, which was explained by Einstein assuming that light is composed of photons and that they interact with electrons as particles.

h f = K + Ф

where fi is the work function of the material

K = hf -Ф

the work function for a given material is constant, therefore let's find the energy of each photon

E = h f

c = λ f

f = c /λ

we substitute

E = h c /λ

Blue light λ = 450 nm = 450 10⁻⁹ m

E = 6.63 10⁻³⁴ 3 10⁸/450 10⁻⁹

E = 4.42 10⁻¹⁹ J

UV light λ = 400 nm = 400 10⁻⁹ m

E = 6.63 10⁻³⁴ 3 10⁸/400 10⁻⁹

E = 4.97 10⁻¹⁹ J

therefore ultraviolet light has more energy than blue light, so electrons must have higher kinetic energy