How Is Work Calculated When Moving a Charge in an Electric Field?

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Homework Help Overview

The discussion revolves around calculating the work done in moving a point charge within an electric field created by another charge. The specific scenario involves moving a 0.2 µC charge from one corner of a square to another, influenced by a 10 µC charge located at the center of the square.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between electric potential and work, questioning the necessity of a specific distance value. Some suggest assuming a side length for the square to see if it cancels out in calculations, while others emphasize the importance of understanding potential energy differences in conservative forces.

Discussion Status

The discussion is active, with participants providing various approaches to the problem. Some have suggested calculating potential energy at different points and comparing them, while others have clarified the concept of work in relation to changes in electric potential. There is no explicit consensus yet, but multiple lines of reasoning are being explored.

Contextual Notes

Participants note the absence of a specific distance value in the problem statement, leading to assumptions about the square's dimensions. The discussion also highlights the conservative nature of electric forces and the implications for calculating work done.

smartdesk
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Homework Statement


What is the work done in moving a 0.2 µC point charge from corner a to b of a square abcd, when a 10 µC charge exists at the center of the square?


Homework Equations


Work or ΔU=q*V
V=kq/r


The Attempt at a Solution


V=kq/r
V=(9.0x10^9)(0.2x10^-6)/r

This is where I get stuck because there is no r given. We can assume that all the sides of the square are equal and the distance to the 10 µC charge is half of that. But I feel like an actual value should be given.
 
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Assume some length of the square side, see if it doesn't cancel out in the final result.
 
I assumed the length of he side of the square to be 0.3m, but it doesn't cancel out. So if the side were 3m, electric potential and work done would be:
V=kq/r=(9.0*10^9)(0.2*10^-6)/3=600 N

ΔU=q*V=(0.2*10^-6)(600)=1.2*10^-4 J
 
i meant 3m not 0.3 m
 
Hi smartdesk

Work out the potential energy of the system when the charge is at a and then again when the charge is at b, and then compare them.
Just use r for the distance.

Notice anything?
 
smartdesk said:
Work or ΔU=q*V

That's not correct. Electric force is conservative, which means work done depends on the difference between potential in the starting and ending point. So the more correct way of expressing it would be ΔU=q*ΔV. Now think what ΔV is.

Edit: ap123 answered while I was composing the answer, but we are aiming at exactly the same thing.
 

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