- #1

- 10

- 0

Then if its moving from A to B, work is done on the electron by an external force?

You are using an out of date browser. It may not display this or other websites correctly.

You should upgrade or use an alternative browser.

You should upgrade or use an alternative browser.

- Thread starter Ivore
- Start date

- #1

- 10

- 0

Then if its moving from A to B, work is done on the electron by an external force?

- #2

jtbell

Mentor

- 15,846

- 4,318

- #3

- 3,788

- 443

- #4

- 10

- 0

_{E}done by the electric field on the electron (with a minus sign thrown in). So if you're talking about the situation in terms of PE and KE, you don't also talk about the W_{E}done by the field, because that would be at least redundant, and at worst, counting the energy involved twice. You talk only about the W done by whatever other (non-conservative) forces are involved in the situation.

So if work is done by electric for on the electron ( aka electron moving from a lower to a higher potential plate ) it is positive while the other way round ( electron moving from higher to lower potential plate ) will have a negative work. Am I right ? Then what about it's EPE and KE , is the EPE/KE the work done ?

- #5

Chandra Prayaga

Science Advisor

- 651

- 149

This confusion arises because the "system" and the "surroundings are not clearly identified. There are two ways of looking at it the problem

Then if its moving from A to B, work is done on the electron by an external force?

1. If the electron is the system, then:

(a) it has kinetic energy

(b) the surroundings do work on it, positive or negative. This is the work done by the electric field

(c) the kinetic energy of the electron changes by an amount equal to the work.

(d) There is no other potential energy in this description.

2. If the system is the electron + the field of the capacitor, then:

(a) there is kinetic energy of the electron

(b) there is potential energy of interaction between the electron and the field, which depends on the position of the electron

(c) the total mechanical energy, the sum of item (a) and item (b), is constant

(d) so as the electron moves, the potential energy changes, and the kinetic energy changes in a way that keeps the total energy constant.

Share: