Calculating Electric Potential Differences

AI Thread Summary
The discussion revolves around calculating electric potential differences when an electron moves in an electric field. The work done by the electric field on the electron is 2.00 x 10^-19 J, leading to the use of the equation ΔV = -W/q. The confusion arises regarding the signs of the potential differences, particularly why the results for (a) and (b) are positive despite the expectation of negative values. The key insight is that since the electron is negatively charged, the work done implies that the potential at point B is actually higher than at point A, resulting in a positive potential difference. Understanding the charge's sign is crucial for correctly interpreting the electric potential differences.
G-reg
Messages
41
Reaction score
0

Homework Statement


When an electron moves from A to B along an electric field line in the figure below, the electric field does 2.00 10-19 J of work on it.

What are the electric potential differences:
(a) VB - VA

(b) VC - VA

(c) VC - VB


Homework Equations


Ok so I know that the equation to use in this case is that of, \DeltaV = \frac{-W}{q}


The Attempt at a Solution


I understand how to choose the equation I've chosen and how to get the right answer. What I don't understand is why the answers to (a) and (b) aren't negative when the equation shows that they should. Can anyone help?
 
Physics news on Phys.org
I don't have all the problem details (not enough to actually work out the problem). But allow me to speculate: Forgot the negative charge of the electron maybe? :wink: There's enough information for me to do the first part.

The given wording was "When an electron moves from A to B [...] the electric field does [positive value] J of work on it."

If the above statement applied to a test charge it means the V(A) is greater than V(B). But we're not dealing with a positive test charge. We are dealing with a negative electron :cool:. So given the negative charge, the statement implies, V(B) is greater than V(a). Therefore,

V(B) - V(A) is positive.
 
Last edited:
I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
Thread 'A cylinder connected to a hanging mass'
Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
Back
Top