# Homework Help: Electron in a uniform electric field.

1. Sep 1, 2005

### evgeniy

First, am I correct on this: If an electron is accelerating upwards in a uniform electric field, then the electric field's direction is pointed opposite, or downwards, right? And to calculate the magnitude and direction of the electric field, I just use the formula

E= k|q|/d^2

The question is: the d, is it the distance from where it starts to where it stops? I ask this because I am aslo given that the acceleration is 4.5m in the first 3 micro-seconds. SO should I divide 3micro-s by 4.5 to find what the d is after 1 s?
Or did I get all this wrong?

Another thing: Can I use the definition of electric field and use : a = F/m or

a = eE/m ??? since I know the charge and the mass and the acceleration???
THanks

2. Sep 1, 2005

### StatusX

Your first sentence is right. But the first formula you gave is for the field of a point particle (at a distance d), while in this problem there is a uniform electric field, like the one set up between the plates of a large parellel plate capacitor. You don't have to worry about the source of the field, though. Just use the acceleration to find the force on the electron and get the field from this, like you suggested at the end.

3. Sep 1, 2005

### evgeniy

Okay I got it. But my final answer is 8.54 * 10^(-18), isn't it too small? Or am I correct?