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Electric Potential NOTES

Electric potential is defined as the work done per unit charge to move a charge from infinity to a point in an electric field. The electric potential at a distance r from a point charge Q is given by the equation V=Q/4πε0r. In a uniform electric field, the electric potential difference V is directly proportional to the distance d between the plates based on the equation E=V/d. Graphs of electric potential and field strength vary with distance from a charged object, with the gradient of the potential graph giving the field strength at each point.

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403 views2 pages

Electric Potential NOTES

Electric potential is defined as the work done per unit charge to move a charge from infinity to a point in an electric field. The electric potential at a distance r from a point charge Q is given by the equation V=Q/4πε0r. In a uniform electric field, the electric potential difference V is directly proportional to the distance d between the plates based on the equation E=V/d. Graphs of electric potential and field strength vary with distance from a charged object, with the gradient of the potential graph giving the field strength at each point.

Uploaded by

JOHANNESKIFENDI
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Electric Potential

To be able to explain what electric potential is and be able to calculate it


To know what the field strength is like in a uniform field and how it is linked to electric potential
To be able to sketch graphs of potential and field strength over distance from surface

Electric Potential, V
The electric potential at a point r from a point charge is defined as:
The work done per unit charge against the field to move a positive point charge from infinity to that point

Q
The electric potential at a distance r from a charge Q is given by: V
4 0 r
The value will be positive when work is done against the field (when like charges are repelling).
The value will be negative when work is done by the field (when opposite charges attract).
In both cases the potential at infinity is zero. Electric potential is a scalar quantity.
Electric Potential is measured in Joules per Coulomb, J C-1
Electric Potential Difference (Also seen in GCSE Physics 2 and AS Unit 1)
Electric potential is the work done per unit charge which can be written like this:
W
V
Q
We came across this equation in the QVIRt lesson of Unit 1. We used it to define the potential difference as the
energy given to each charge. From what we have just defined we can now update our definition of potential
difference. Potential difference is the difference in electric potential between two points in an electric field.
The work done to move a charge from potential V1 to potential V2 is given by:
W  Q(V2  V1 ) which can be written as W  QV
Uniform Fields
In a uniform field like that between two conducting plates the field strength is
constant as we have already seen. Now that we understand electric potential we can
use an equation for the field strength in a uniform field.
V
E Where V is the potential difference between the plates and d is the separation of the plates.
d
Electric Field Strength can be measured in Volts per metre, V m-1
Graphs
Here are the graphs of how electric
field strength and electric potential
vary with distance from the centre
of a charged sphere. In both cases R
is the radius of the sphere.

The gradient of the electric potential


graph gives us the electric field
strength at that point. To find the
gradient at a point on a curve we
must draw a tangent to the line then
calculate the gradient of the
tangent:
y V
gradient   E
x r
www.physicstutoronline.co.uk
If we rearrange the equation we can see where we get the top equation for electric potential.
V Q Q Q
E  Er  V sub in the equation for E  r  V  r V  V
r 4 0 r 2
4 0 r 2
4 0 r

www.physicstutoronline.co.uk

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