|By Jjax (Jjax) on Sunday, May 02, 2004 - 04:36 pm: Edit|
My AP Physics teacher gives us these damned worksheets with insainly difficult problems, and I need help.
An electron is fired at a speed of v0- 5.6 x 10^6 m/s at an angle of theta0= -45(degrees) between two parallel conducting plates that are D = 2.00 mm apart as shown below. If the potential difference between the plates is (delta)V = 100 V, determine:
A. How close, d, the electron will get to the bottom plate and,
B. where the electron will strike the upper plate.
Any help, even if you only have the time/expertise to hint at the answer or solve only part of the problem would be greatly appreciated.
|By Jszab (Jszab) on Sunday, May 02, 2004 - 04:59 pm: Edit|
I am assuming that bottom is minus, and top plus. You shoul have mentioned it.
You should mention about gravity, but it will not have big influence on result.
Follow the steps, I will try to explain it to You. Not to write down :P. ;)
1. When the electron is fired between the plates, the electric force starts to pull [or push] him up.
2. Because, when one plate is pulling the electron with a force inversly proportional to distance from the plate, and second pushing, with the same principle, the overall result is that:
Force affecting between plates has the same direction and magnitude [exception - ends. In this case we do not have neccesary data to do it with ends. So omit it as too difficult ;] ]
next in a minute
|By Transferkid (Transferkid) on Sunday, May 02, 2004 - 04:59 pm: Edit|
I'll give you a hint:
From the deltaV you can determine the E-field( V=E*D), and from the E-field, you can determine the electrostatic force on the electron(F=q*E, with q the elementary charge of the electron).
From here on, your problem is in fact a mechanics problem. You can determine the acceleration of the electron due to the electrostatic force, and hence an equation of velocity as a function of time( v(t)=int(a)dt), and therefore an equation for the displacement of the electron as a function of time(x(t)=int(v)dt, naturally). Once you've done that, the answers to A and B can come easily.
|By Jszab (Jszab) on Sunday, May 02, 2004 - 05:05 pm: Edit|
3.The force started to acting on the electron, so it will move towards upper plate.
This force - gravity force = Force that we seek for
W = eED >> use it to find this force.
4. Now sketch trajectory, it will look as: [rotate your page by 180 degrees] as trajectory of thrown ball, in gravity field.
|By Jszab (Jszab) on Sunday, May 02, 2004 - 05:14 pm: Edit|
Now solve, as for kinetics gravity problem [for the first task, or make from dynamics, and energy.]
Second, is easiest to determine horizontal velocity, and time of "flight" , and thus distance, simply by taking V/t.
I hope You understand it now .
It is the same problem, as any other in dynamics. Nothing new.
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