# B Photoelectric effect

1. Mar 18, 2016

### Gajan1234

Can someone explain what is stopping potenial is and can explain the formula : e × Vs. Does the v stand for voltage

2. Mar 18, 2016

### Staff: Mentor

3. Mar 19, 2016

### Jilang

When a photon is absorbed some of its energy is used to free the electron and what is left over is given to the freed electron as kinetic energy. The stopping potential slows the electron down and if the potential is high enough the electrons won't make it to the detector. The value of the potential at which this happens occurs when the work done by the electric field is equal to the kinetic energy. This value is eV xS, so yes V is the potential (or voltage difference).

4. Mar 20, 2016

### cryora

Is that exactly true? Or is there a range of possible leftover energy transferred from the photon to the electron as kinetic, from 0 up to the entire leftover energy? I don't have the textbook with me, but in Serway's "Modern Physics", he mentions a maximum kinetic energy for the freed electron being equal to the leftover photon energy, which implies there are probably other processes which might take away said energy.

5. Mar 20, 2016

### vanhees71

6. Mar 20, 2016

### Staff: Mentor

In the (over)simplified treatment of the photoelectric effect that you commonly find in introductory textbooks like that, the "energy used to free the electron" is not the same for each electron. Crudely and simplistically speaking, think of it as reflecting how "deeply buried" the electron was in the material. A certain minimum energy is needed to free the electron, corresponding to a maximum kinetic energy after ejection.