# Time of flight of an accelerated electron in a television tube

1. Mar 21, 2005

### dranger35

I was given this problem for homework.

Assume you have a television tube that is about 0.3 m from cathode to screen, and electrons are accelerated uniformly through 20 kV – the electric field is constant. How long does it take for the electrons to travel from the cathode to the screen? The electron mass is 9.11x10-31 kg.Assume you have a television tube that is about 0.3 m from.

Can any1 let me know what equation to start off with adn one to find the time. Thanks

2. Mar 21, 2005

### joshuaw

You should look at the force due to an electric field, F(vector)=q(scalar)*E(vector)
Now that you have the force due to the electric field, simply use Newton's second law to get the acceleration.
With the acceleration and the distance to the screen, you should be able to get the time of flight.

3. Mar 21, 2005

### dranger35

Yea but how do I know the F if I don't know q or E? Thanks again, I'm really confused with it.

4. Mar 21, 2005

### Crosson

In this case you may use:

V = E*d