# A metal emits electrons that possess a kinetic energy = #3.1 xx 10^-19# J/electron when exposed to radiation whose frequency is #2.4 xx 10^15# Hz. What is the threshold frequency of the metal in Hz?

##### 1 Answer

I got:

#### Explanation:

We know that the metal should emit electrons with kinetic energy

where

The threshold frequency will be the one that, carried by a photon, will give an energy that matches exactly the Work function (needed to free the electron BUT not to give it kinetic energy to actually fly away!).

So we get:

and when we have

From the first, using our data, we get (for each electron):

so that rearranging:

into the second equation:

rearranging: