# Parellel platers help

1. Jul 20, 2009

### mvk1

Parellel platers help :(

An electron with a velocity of 3.00 3 106 m/s [horizontally]
passes through two horizontal parallel plates. The magnitude of the electric field between the
plates is 120 N/C. The plates are 4.0 cm across. Edge
effects in the field are negligible.
(a) Calculate the vertical deflection of the electron.
(b) Calculate the vertical component of the final velocity.
(c) Calculate the angle at which the electron emerges

Diagram: http://img50.imageshack.us/img50/6418/problemo.jpg [Broken]

Formulas: http://img339.imageshack.us/img339/186/formulae.jpg [Broken]

Last edited by a moderator: May 4, 2017
2. Jul 20, 2009

### queenofbabes

Re: Parellel platers help :(

Well....your own thoughts? What have you worked out?

3. Jul 20, 2009

### mvk1

Re: Parellel platers help :(

ive tried to comprehend this but i am failing how do i find vertical deflection because d is already given

4. Jul 20, 2009

### queenofbabes

Re: Parellel platers help :(

What do you mean by d? Can you see that there will be a force causing the electron to be deflected? (Think attraction/repulsion)

5. Jul 20, 2009

### mvk1

Re: Parellel platers help :(

even if i calclate fe it is ont the distance of deflection..

6. Jul 20, 2009

### queenofbabes

Re: Parellel platers help :(

How would you find a distance from the force? Hint: For how long is the force acting on the electron?

7. Jul 20, 2009

### mvk1

Re: Parellel platers help :(

and when it says the plates are 4.0 cm across does it mean each plate or total plates

8. Jul 20, 2009

### mvk1

Re: Parellel platers help :(

F=qE
F=1.6x10^-19 C x 120 N/C
F=1.92x10^-17 N

Last edited: Jul 20, 2009
9. Jul 20, 2009

### mvk1

Re: Parellel platers help :(

10. Jul 20, 2009

### queenofbabes

Re: Parellel platers help :(

Good, you have your force. I'm sure what the question meant is that the length of the plates is 4cm, such that the horizontal distance travelled by electron under the influence of the E field is 4cm.

Now then, how would you find a distance from the force? Hint: For how long is the force acting on the electron?

11. Jul 20, 2009

### mvk1

Re: Parellel platers help :(

update:
i have found the accelaration using fnet =ma
since it is an electon mass is 9.1x10^-31
a=1.92x10^-17 N / 9.1x10^-31kg
a=2.1x10^13m/s2

BUT isnt this impossible ebacause it cant accelarate more than the speed of light

12. Jul 21, 2009

### queenofbabes

Re: Parellel platers help :(

Acceleration and speed cannot be compared like that. You simply can't travel faster than light. You can accelerate however quickly you want (as long as you have the force to do it)

You're on the right track.