Determine the work function A of electrons from sodium if the red border of the photoelectric effect is 500 nm.

λcr = 500 nm = 500 * 10 ^ -9 m.

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

s = 3 * 10 ^ 8 m / s.

Av -?

Incident light is an electromagnetic wave that can be thought of as a stream of photons that carry energy.

The work function of electrons from the surface of sodium Ab is called the work that the photons of the incident light do in order to snatch electrons from the surface of the metal. The photons of light must have energy Eph sufficient to make this pulling out: Eph = Av.

The incident photons have energy Eph, which we express by the formula: Eph = h * s / λcr, where h is Planck’s constant, c is the speed of the electromagnetic wave in vacuum, λcr is the red wavelength of photons for sodium.

Av = 6.6 * 10 ^ -34 J * s * 3 * 10 ^ 8 m / s / 500 * 10 ^ -9 m = 3.96 * 10 ^ -19 J.

Answer: the work function for sodium is Av = 3.96 * 10 ^ -19 J.