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## JenniferSmart1 Group Title Question one year ago one year ago

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1. JenniferSmart1 Group Title

|dw:1361317472233:dw|

2. JenniferSmart1 Group Title

|dw:1361317624407:dw|

3. JenniferSmart1 Group Title

$W=-\triangle U=-\int F\cdot dl=-\int_{x_1}^{x_2} Fdx=-kq_1q_2\int_{x_1}^{x_2}\frac{dr}{r^2}=-\frac{-kq_1q_2}{r}$ I figured that $q=\sigma A$ I'm told that the charge densities are equal and opposite on the two large plates.

4. JenniferSmart1 Group Title

Oh and we're moving an electron from the negatively charged plate to the positively charged plate.

5. JenniferSmart1 Group Title

@TuringTest

6. JenniferSmart1 Group Title

I calculated the electric field already

7. TuringTest Group Title

what is the question?

8. JenniferSmart1 Group Title

I have to calculate the work done to move an electron from the negative plate to the positive plate.

9. JenniferSmart1 Group Title

|dw:1361318208383:dw| This is the force I need to overcome correct?

10. JenniferSmart1 Group Title

|dw:1361318290447:dw|

11. JenniferSmart1 Group Title

My class is about to start...

12. TuringTest Group Title

there is no resistance force to overcome, just the inertia of the electron moving due to the E field

13. JenniferSmart1 Group Title

but the electric field is pointing in the opposite direction of where the electron is moving to

14. TuringTest Group Title

but the E-field points in the direction that a *positive* test charge would move. After all, an electron wants to go from negative to positive, right? Like repels like and so forth...

15. JenniferSmart1 Group Title

Oh I see...

16. JenniferSmart1 Group Title

In that case: $W=-\triangle U=-q\triangle$ q= is the charge of an electron correct?

17. JenniferSmart1 Group Title

@phi

18. JenniferSmart1 Group Title

oops! $W=-\triangle U=-q\triangle V$

19. TuringTest Group Title

I would say the elementary charge is $$q=-e$$$W=-\int(-e)\vec E\cdot d\vec\ell=-e\int Edx$Note that three negatives multiply to give a negative result. One negative from the charge, one from the fact that a positive charge moving along the E field lines goes down in energy, and one from the fact that E and the direction of motion are antiparallel.

20. JenniferSmart1 Group Title

so shouldn't use the relationship I wrote earlier

21. JenniferSmart1 Group Title

I'm given the potential difference between the plates

22. JenniferSmart1 Group Title

I mean shouldn't *I use the relationship I wrote earlier

23. JenniferSmart1 Group Title

sorry typo

24. JenniferSmart1 Group Title

I mean if I'm given delta V and I know e ....I should be able to just multiply those to get delta U

25. TuringTest Group Title

right, then that's all

26. JenniferSmart1 Group Title

oh and http://en.wikipedia.org/wiki/Joule are $C\cdot V=Joules$ correct?

27. TuringTest Group Title

coulombs*volts=jouls, yeah

28. JenniferSmart1 Group Title

Thanks Max!

29. TuringTest Group Title

Welcome "Jennifer/sophya"

30. JenniferSmart1 Group Title

LOL!!!!!! Not even close haha

31. JenniferSmart1 Group Title

since KE=U the kinetic energy would be the same correct?