# Homework Help: Electron- Potential/ speed

1. Sep 16, 2007

### physicsstar26

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

An electron (m= 9.1*10^-31 kg, q=-1.6*10^-19C) moving with a speed of 10^6 m/s enters the region between two parallel and oppositely charged metal plates across which the potential difference is 10V. Will the electron hit the opposite plate- show calculations on how you would solve this.

2. Relevant equations

Va-Vb= E*dL
q*V= (1/2)mv^2

3. The attempt at a solution

Do you first find the potential then solve for the velocity?

2. Sep 16, 2007

### dynamicsolo

There seems to be a detail missing in order to decide whether the electron will strike a plate. What is the direction of the electron's initial velocity relative to the plates? How far away from either plate does it enter? This is rather ambiguous as it stands now.

3. Sep 17, 2007

### physicsstar26

There is just a picture with two lines representing the two parallel plates, the first line is labeled 10V and the second line is labeled 0V. There is a small circle in front of the 10V line with an arrow pointing to the right. That is all the information that is provided on the practice test.

4. Sep 17, 2007

### Astronuc

Staff Emeritus
If the electron enters the region from the positive potential, it will decelerate, since it traveling against the electric field.

One could compare the kinetic energy of the electron against the potential difference of 10V.

If the kinetic energy is less the 10 eV, the electron will not reach the negative plate.

The change in kinetic energy of the electron is related to qV.