Planck's constant (the photoelectric effect)

Plotting the maximum photo-electron energy against frequency (f) gives a straight line.

Emax = hf -W

... where h is Planck's constant and W is the work function.

If the stopping voltage, is 1.72 Volts, with a work function of 0.6 eV, find the minimum photon energy, and wavelength, required to eject electrons from the cathode.

hf = Emax + W

= 2.32 eV

Converting the photon energy to Joules and using the wave equation f.=.c/l ....lmin is given by ...

lmin = ch/ (2.32 x 1.6x10-19)

= 3.0x108 x 6.63x10-34/ (2.32 x 1.6x10-19)

= 5.4x10(8 - 34 +19)

= 5.4x10-7 meters (in the green)