Find the longest light length at which the photoelectric effect can occur for platinum.

Find the longest light length at which the photoelectric effect can occur for platinum. The work function of electrons is 1.8 * 10 * -19 J

h = 6.6 * 10 ^ -34 J * s.

C = 3 * 10 ^ 8 m / s.

Av = 1.8 * 10 ^ -19 J.

λ -?

The photoeffect will be observed when the photon energy Eph is sufficient to knock out electrons from the metal surface Ab: Eph = Ab.

The energy of the incident photons Eph is expressed by the formula: Eph = h * C / λ, where h is Planck’s constant, C is the speed of light, λ is the wavelength of the photons.

h * C / λ = Av.

The wavelength of photons λ = is expressed by the formula: λ = h * C / Av.

λ = 6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 1.8 * 10 ^ -19 J = 11 * 10 ^ -7 m.

Answer: the longest photon wavelength is λ = 11 * 10 ^ -7 m.