Which Photon Energy Can Overcome a 3.00 eV Work Function?

[sgoeke]

Homework Statement

Of the following energies for photons, which is the least energy that could result in photoeletron production if the work function is 3.00 eV?
a. 1.50 eV
b. 2.90 eV
c. 3.50 eV
d. 6.01 eV

Homework Equations

KE = E - W

The Attempt at a Solution

I don't know where to go with this. please help!

 

[kuruman]

KE = E - W

What do the three terms in this equation stand for? Which ones can be identified with what is given?

 

[sgoeke]

KE is the kinetic energy, E is the energy of the photon (E=hf or E=hc/lambda), and W is the work function. 3 eV is the work function (W). We're looking for E. But I don't know what KE would be.

 

[kuruman]

KE is the kinetic energy, E is the energy of the photon (E=hf or E=hc/lambda), and W is the work function. 3 eV is the work function (W). We're looking for E. But I don't know what KE would be.

No you don't. Go down the list of possible answers starting with (a). Would a 1.50 eV photon produce a photoelectron? If so, what would would the photoelectron's KE be?

 

[sgoeke]

How do you know you produce a photoelectron?

 

[kuruman]

How do you know you produce a photoelectron?

Can a 1.50 eV photon produce a photoelectron if the work function is 3.0 eV? The answer is "yes" or "no". If you don't know how to answer this question then you do not understand the photoelectric effect, specifically what "work function" means. You need to review the photoelectric effect by reading your textbook or getting on the web. If you are still confused, explain what you do understand and what you don't and someone will help you.

 

[sgoeke]

The KE depends on the light frequency and the critical frequency is the photons whose energy is equal to the work funciton. I guess I'm really not making the connection for this problem even after reading this section of my textbook multiple times.

 

[kuruman]

The idea behind the photoelectric effect is very simple. Think of energy as money. The work function is the exit fee that an electron has to pay to leave the metal. A photon comes along and gives all the money it has to an electron in the metal. Two things may happen as a result.
1. If the electron has more money than the exit fee, it pays it, leaves the metal and takes with it the change as kinetic energy.
2. If the electron does not have enough money to pay the exit fee, it stays where it is and the photon's money is shared in some fashion within the metal.

Now again, can you answer the question "Can a 1.50 eV photon produce a photoelectron if the work function is 3.0 eV?"

 

[sgoeke]

So the energy would need to be larger than the work function? So the least amount of energy for the ones given would be 3.5?

 

[kuruman]

So the energy would need to be larger than the work function? So the least amount of energy for the ones given would be 3.5?

Bingo!

 

[sgoeke]

Thanks...that really really helped!