In a photoelectric-effect experiment, the maximum kinetic energy of electrons is 3.0 ev . when the wavelength of the light is increased by 50%, the maximum energy decreases to 1.2 ev . what is the work function of the cathode? what is the initial wavelength?

2.4 eV

230 nm

Explanation:

The equation for the photoelectric effect is:

Where

h: Planck's constant (4.13e-15 eV * s)

f: frequency

phi: work function

This can be omdified to:

Where

c: speed of light in vacuum

lambda: wave length

We can set two equations:

(1)

(2)

If we multiply equation (2) by 1.5 we obtain

(3)

If we substract eq (3) from eq (1)

Knowing this we can calculate the original wavelength

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