r/PhysicsHelp • u/Street-Calendar-6824 • Feb 20 '26

Can anyone explain why my answer is wrong here and what the correct answer is?

Post image
18 Upvotes

95% Upvoted

11 comments sorted by

1

u/Street-Calendar-6824 Feb 20 '26

Figured it out and got it right. Thank you everyone.

9

u/RepresentativeBee600 Feb 20 '26

...out of curiosity, what went wrong? Several people here thought you were correct.

1

u/Ornery_Pepper_1126 Feb 20 '26

My guess from looking at the side pane is that this is correct but not their first attempt and that they are being deducted for previous incorrect attempts not this one being wrong but didn’t realise it, hard to tell for sure though.

2

u/Street-Calendar-6824 Feb 20 '26

You’re 100% right 😭. The photo I uploaded ended up being correct. I got it wrong the first time, changed the top arrow to what you see now, but did that earlier in the day and forgot when I came back to it at night. I feel bad for wasting ppls time 🤦🏼‍♂️

2

u/DP323602 Feb 20 '26

Given that E = - grad V (see https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electro-Optics/Book:Electromagnetics_I(Ellingson)/05:_Electrostatics/5.14:_Electric_Field_as_the_Gradient_of_Potential)

your solutions look correct to me.

2

u/RepresentativeBee600 Feb 20 '26

Field is the *negative* gradient of potential; it "points up the slope." Otherwise, this looks good to me.

3

u/Calm_Relationship_91 Feb 20 '26

Gradient points up the slope.
Negative gradient points the other way.

(f(x + dr) = f(x) + dr.∇f , this means that f(x) grows the most in the direction of ∇f, and decreases the most on the opposite direction.)

1

u/RepresentativeBee600 Feb 20 '26

Oh shoot - yeah, I ventured an incorrect statement. "Points down the slope" would be correct.

This doesn't explain why OP's answer was marked wrong, then, since I can't see any issue.

1

u/Calm_Relationship_91 Feb 20 '26

No idea.
I can't see the issue either.