Lecture ( 7 ) Electric Potential and Capacitance

Electric Potential ( V )
The work per unit of charge required to move a charge from a reference point to a specified point, measured in joules per coulomb or volts. The static electric field is the negative of the gradient of the electric potential.






Equipotential Surfaces



Electric Pontential and Electric Potential Energy
The change in potential energy of a charge ( q ) moving from point (i) to point (f ) is equal to the work done by the applied force , which is equal to minus the work done by the electric field , which is related to the difference in electric potential:


We move a proton from point (i) to point (f) in uniform electric field ,as shown.

Electric Potential of a Point Charge

Note: if ( Q ) were a negative charge ,( V ) would be negative.
Electric Potential of Many Point Charges
Electric potential is a SCALAR not vector , therefore just calculate the potential due to each individual point charge, and add together ( Make sure you get the SIGNS correct )





2.8 Capacitance
Energy is store in the electric field that exists between the plates when the capacitor is charged.








Stored Energy