Determine the red border of the photoelectric effect for potassium if the work function is 2.15 eV.

The red border of the photoelectric effect is found by the formula ν (ny min.) = A (out) / h, where ν (nu min.) Is the red border of the photoeffect, A (out) is the work function of the photocathode, h is Planck’s constant, which is h = 6.626 * 10 ^ (- 34).
Since A (out) is measured in J, it is necessary to convert 2.15 eV to J:
1 eV – 1.6 * 10 ^ (- 19) J
2.15 eV – 3.44 * 10 ^ (- 19) J
Substitute the values in the formula and then we get ν = 3.44 * 10 ^ (- 19) /6.626*10 ^ (- 34) = 0.519 * 10 ^ (15) Hz = 519 THz
Therefore, ν = 519 THz (terahertz).