Determine the red border of the photoelectric effect for potassium if the work function is 2 eV.

Av = 2 eV = 3.2 * 10 ^ -19 J.

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

C = 3 * 10 ^ 8 m / s.

λcr -?

The red border of the photoelectric effect λcr is the maximum radiation wavelength at which the emission of electrons from the metal surface begins to be observed. The energy of the incident photons Eph goes only to pulling Ab from the metal surface: Eph = Av.

The energy of 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 photons.

h * C / λcr = Av.

λcr = h * C / Av.

λcr = 6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 3.2 * 10 ^ -19 J = 6.19 * 10 ^ -7 m.

Answer: the wavelength of the red border for this metal is λcr = 6.19 * 10 ^ -7 m.