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

divide the right side by the left side

0.024÷1.2=0.02 for example