#### RJLiberator

Gold Member

- 1,093

- 62

**1. Homework Statement**

We are performing a lab on the photoelectric effect tomorrow and have some pre-lab questions.

**1:**If an electron must use an energy equal to the work function of the phototube cathode, in order to escape the cathode's surface, how much kinetic energy does it have once it escapes?

**2:**What is the energy required for an electron of charge -e to travel across a potential difference of -V?

**3:**IF there are two frequencies of light with v_1> v_2>0, in a light beam shining on a phototube whose work function is x_0 at what level of applied voltage across the phototube will all the electrons which received a photon of frequency v_2 and v_1 be stopped? Which of these voltages are greater?

**2. Homework Equations**

c = wavelength * frequency

E=hv, h=plancks constant

**3. The Attempt at a Solution**

**My answers/guesses:**

1:Energy = hv-work function where v is the frequency. This seems simple enough to me, but I have not studied this in quite some time, so I was looking for confirmation here.

1:

**2:**E=V/d where d is the seperation. So this would mean V=E*d and since #1, we see V=(hv-workfunction)*d.

**3:**Since equation in answer 2 shows us that the higher the frequency the higher the voltage, we conclude that the voltage for v_1 is greater. Not sure how to answer the part on applied voltage...