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### Course: Physics library>Unit 11

Lesson 3: Electric potential energy, electric potential, and voltage

# Electric potential from multiple charges

In this video David shows how to find the total electric potential at a point in space due to multiple charges. Created by David SantoPietro.

## Want to join the conversation?

• David says that potential is scalar, because PE is scalar -- but vectors must come into play when we place a charge at point "P" and release it?

The calculation for potential at point "P" is +5,250 J/C, so if we place a +1 C charge there, then it will have 5,250 J of PE. Once we place that +1 C charge there and release it, the 5,250 J of PE will convert into KE and the charge will move -- but it will move in a specific, predictable path -- won't it?

How can we determine the path that any charge would take upon being placed in that position?
• Can the potential at point P be determined by finding the work done in bringing each charge to that point?
• just one charge is enough. one unit charge brought from infinity.

then the potential is the work done, (per unit charge) in bringing it from infinity to that point

ok?
• About this whole exercise, we calculated the total electric potential at a point in space (p) relative to which other point in space?
And the final result tells us that a charge of 1 Coulomb on the point p can do 5250J of work ("displacement against a force") more than any other point?
Thanks!
• the potential at infinity is defined as being zero.

The potential at a point is the amount of work it will do (or will be done to it) in moving it to infinity. Depending on the sign of charge
• In this video, are the values of the electric potential due to all the three charges absolute potential (i.e. with respect to infinity)?
(1 vote)
• there is no such thing as absolute potential but when you use the equation kQQ/r you are implicitly setting zero at infinity.
• So if we're trying to calculate a scalar quantity, we plug in signs based on charge. If we're trying to calculate a vector quantity, we plug in signs based on direction. Correct?
• Is there any thing like electric potential energy difference other than electric potential difference ? please answer soon .
• Sorry, this isn't exactly "soon", but electric potential difference is the difference in voltages of an object - for example, the electric potential difference of a 9V battery is 9V, which is the difference between the positive and negative terminals of the battery.

Electric potential energy difference would be the difference in potential energies at a point in space - but I'm not really sure what it would look like. I doubt you'll ever see the term "electric potential energy difference" anywhere so no need to worry about that :-)
• If i have a charged spherical conductor in side another bigger spherical shell and i made a contact between them what will happen ?
does they balance at equal electric potential ?
or the charge goes to the outer shell ?
and why?
(1 vote)
• Why is the electric potential a scalar? Which way would a particle move?
(1 vote)
• Electric potential is just a value without a direction. The direction of the changed particle is based the differences in the potential not from the magnitude of the potential. This change in potential magnitude is called the gradient.
(1 vote)
• 1. If the distance given in a problem is in cm (rather than m), how does that effect the "j/c" unit (if at all)?
2. If I wanted to calculate how much energy it takes to move one of these charges from its current place to a place a few meters over, could I just say that movement would take the EP measurement of one point (ex: 2,250J/C for V1) times the amount of Coulumbs the point has? AKA: How would I calculate the amount of energy needed to move a point?
(1 vote)
• 2. Two point charges each of magnitude q are fixed at the points (0, +a) and
(0, –a) in the Cartesian coordinate system.
i. Draw a diagram showing the positions of the charges.
ii. What is the potential Vo at the origin?
iii. Show that the potential at any point on the x-axis the potential is
given by
   
2 2 2 2
0
0
1 2
4 2
q q V
a x a x  
  
 
iv. At what values of x is the potential one half of that at the origin?
v. Sketch the variation of the potential along the x-axis as a function
of x.
(1 vote)