What is the relationship between electric field strength and the potential gradient?

  • #1

Homework Statement



What is the relationship between electric field strength and the potential gradient?



Homework Equations





The Attempt at a Solution



This is my Calc based Physcis lab question but I am at a total loss. I do not understand what potential gradient is in the first place. From google I figured out that it is rate of change.

My understanding is as the gradient decreases the electric field strength increases. But I know that by looking at graph I have made. I do not understand why is it so theoritically.

Please help!

Thanks,

Arshad
 

Answers and Replies

  • #2
370
0


http://en.wikipedia.org/wiki/Potential_gradient

Check that out, thinking about it more mathematically;

You agree that the electric potential is given by [tex] v = \frac{kq1q2}{r^2} [/tex] , right?

Now when looking for the potential gradient, you're looking for the change of potential per distance moved away, so if for instance you plotted a graph of electric potential against distance away, the potential gradient is basically the gradient of that graph, so [tex] \frac{dV}{dr} [/tex] .

Now find [tex] \frac{dV}{dr} [/tex] where [tex] V = \frac{kq1q2}{r^2} [/tex]

you might see a similarity with E.
 
  • #3


THanks! :) This makes much more sense to me now! :)

So basically, the more steeper the gradient (or equipotential lines) is, the mroe stronger the electric field gets, right?
 
  • #4
collinsmark
Homework Helper
Gold Member
2,914
1,296


http://en.wikipedia.org/wiki/Potential_gradient

Check that out, thinking about it more mathematically;

You agree that the electric potential is given by [tex] v = \frac{kq1q2}{r^2} [/tex] , right?

Now when looking for the potential gradient, you're looking for the change of potential per distance moved away, so if for instance you plotted a graph of electric potential against distance away, the potential gradient is basically the gradient of that graph, so [tex] \frac{dV}{dr} [/tex] .

Now find [tex] \frac{dV}{dr} [/tex] where [tex] V = \frac{kq1q2}{r^2} [/tex]

you might see a similarity with E.
Actually that's not quite right.

[tex] V = - \int _P E \cdot dl, [/tex]

Where P is an arbitrary path (i.e. V is the "voltage" between the two endpoints of the path),

Not that it matters much for this problem, but the potential of a point charge, with respect to infinity, is:

[tex]
V = -\int _{\infty} ^{r} \frac{1}{4 \pi \epsilon _{0}} \frac{q}{r' ^{2}} dr' [/tex]

[tex] = \frac{1}{4 \pi \epsilon _{0}} \frac{q}{r} [/tex]

Note that it is a function of 1/r, not 1/r2.

But none of that really matters for this problem.

I think the question is asking you to look up a formula in your book, and compare it to the gradient of the potential.

The gradient of a scalar field is specified by the [tex]\nabla[/tex] operator (called the "del" operator). So the gradient of the potential is specified by [tex] \nabla V [/tex].

So look in your textbook for something that relates [tex] \nabla V [/tex] to [tex] E [/tex]. Although I haven't seen your textbook, I'm confident this relationship is in there.
 
  • #5


Well, there is one:

E = -dV/dl

OR

V = - integral [ E dl]

Thanks soo much to both of you for yours' help!! :)
 
  • #6
370
0


Yeah >.< sorry Arshad, replace the 1/r^2 with a 1/r in my post, foolish on my part.
 
  • #7


Is any one here to explain the Result of electric field as potential gradient
E= -dV/dr
Please Explain this result
what is affect on electric intenity as Electric potential difference increase or Decrease
And aslo what is affect on electric intenity distance r increase or Decrease
Please Help me?
 

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