The discussion revolves around the potential energy of an electron in the vicinity of a negative source charge, specifically addressing the initial potential energy of the electron and its implications in a physics problem involving kinetic and potential energy. The scope includes conceptual clarification and technical reasoning related to electrostatics and energy conservation principles.
Participants do not reach consensus on the initial potential energy of the electron. There are competing views regarding the interpretation of the problem and the role of initial conditions in energy calculations.
There is a lack of clarity regarding the specific problem being discussed, which may contribute to the confusion over the initial potential energy. The discussion also reflects differing interpretations of the reference points for potential energy in electrostatics.
This discussion may be useful for students and educators in physics, particularly those exploring concepts of potential energy, kinetic energy, and electrostatics in the context of homework or coursework problems.
. Why is that so?Murphy.T said:In solving you use ke = pe
Chandra Prayaga said:You said, . Why is that so?
So, if you don't use it, how will you solve the problem?Murphy.T said:Well maybe you don't have to, but on the key where I got the question that's what was done.
Murphy.T said:If an electron starts from rest 85.0 cm from a negative fixed source charge of -0.135 micro coulombs we use the equation ke final - ke intial + pe final - pe intial. In solving you use ke = pe which appears to cancel out the inital kinetic and potential energy but how can the initial potential energy of an electron near a negative source charge be zero?
Right it wasn't the problem I was wondering about so much as the concept of a negative charge with initial potential energy being zero near another negative charge, but you're saying it does ( have initial potential energy) and it's just the change in potential energy equals the change in kinetic, which makes sense now.ZapperZ said:This is VERY confusing, mainly because you did not indicate the exact problem and what exactly you were asked to find!
First of all, if the electron is initially at rest, then what's the brouhaha over "initial KE"? Isn't this zero?
Secondly, where is this "final" condition occurring? Is it at some arbitrary distance from the fixed source charge?
What you should have been aware of (and this is the physics part of the problem), is that the change in PE will equal to the change in KE. It is not the absolute value of each of these quantities. Since initial KE is zero, then this change in PE will be equal to the final KE. This is the whole point of the problem, and it is the concept that is being tested.
This sounds like a HW/Coursework problem, and it is, it has been posted in the wrong part of PF.
Zz.
Murphy.T said:Right it wasn't the problem I was wondering about so much as the concept of a negative charge with initial potential energy being zero near another negative charge, but you're saying it does and it's just the change in potential energy equals the change in kinetic, which makes sense now.
Also yes the final position is arbitrary. I understand the question which was why I posted here not in homework I was unsure.
Sorry I (didn't) mean to say that you said initial PE was zero.ZapperZ said:No, I never said that the initial potential energy is zero.
I said that since the electron started at rest, the initial KINETIC ENERGY is zero.
PE is zero only at zero electrostatic potential, and in this case, it is zero at infinity. The electrostatic potential isn't zero when the electron is near the fixed charge.
Zz.
Murphy.T said:Sorry I mean to say that you said initial PE was zero.
I was confused because in the key they said initial PE was zero and they used the final PE for the equation KE final - KE intial + PE final - PE intial = 0
I apologize for my typing errors, I know initial potential energy is not zero but I am being told otherwise, I think I get it now thanks for your help.ZapperZ said:BUT I NEVER SAID THAT!
I do not know how else to say this. INITIAL POTENTIAL ENERGY IS NOT ZERO!
Do I have to use bigger fonts now to make my point?
Zz.