1. Sep 11, 2008

### heinsmit

1. The problem statement, all variables and given/known data

A clean surface of potassium in a vacuum is irradiated with light of wavelength 5.5 x10 -7 m and electrons are found just to emerge, but when light of wavelength 5.0 x 10 -7 m is incident, electrons emerge with energy 3.62 x 10-20 J. Estimate a value for Planck's constant.

I understand the basics like finding work functions and Einstein's equation, but I haven't got a clue with this one. This is an emergency!

2. Sep 11, 2008

### edziura

Once the energy of the incident photons is sufficient to overcome the work function, any additional energy is converted into the KE of the electrons. The energy of a photon is E = hc/$$\lambda$$.

We can therefore estimate h from the data you have by writing

$$\Delta$$ E = h c / ($$\Delta$$$$\lambda$$).

Solve for h, and substitute your data.