1. Electrical Energy and Current
Electric Potential

2. Electrical Energy and Electric Force
Work is done on a charge q as it is moved from a position A to position B when the charge is in an electric field E.
This gives the charge electrical potential energy.
When the charge is released from position B, the electrical force, qE, accelerates the charge through the distance d. The potential energy the charge possesses is then changed into kinetic energy.

3. Electrical Energy and Electric Force
Electrical potential energy – potential energy associated with an object due to its position relative to a source of electric force
Measured in joules (J) just like any other form of energy
In atomic and nuclear physics – measured in electron volts (eV)
1eV = 1.60*10-19J
Results from interaction of two objects’ charges
Is a form of mechanical energy
ME = KEtrans + KErot + PEg + PEelastic + PEelectric

4. Electrical Energy and Electric Force
Electrical potential energy can be associated with a charge in a uniform field
Uniform field – a field that has the same value and direction at all points
Electrical potential energy for a charge in a uniform electric field
Electrical potential energy = - (charge * electric field strength * displacement from the reference point in the direction of the field)
PEelectric = -qEd
d is only relevant when it is parallel to the electric field
May have to use right triangle functions to get the parallel component of motion

5. Electrical Energy and Electric Force
+ charge
charge
In same direction of electric field
Loses PEelectric
Gains PEelectric
In opposite direction of electric field

6. Electrical Energy and Electric Force
Electrical potential energy for a pair of charges
Electrical potential energy = Coulomb constant * charge 1 * charge 2 / distance
PEelectric = kCq1q2/r
kC = 8.99*109 N*m2/C2
When the charges have the same sign, their potential energy is positive, which corresponds to a repulsive force. When the charges have unlike sign, their potential energy is negative, which corresponds to an attractive force. As like charges are separated, the potential energy of the system decreases.

7. Changing Electrical Potential
Electric potential – the electric potential energy associated with a charged particle divided by the charge of the particle
Symbolized by V and measured in volts (V)
Since larger charges have greater electric potential energies than smaller ones, the ratio of electric potential energy to charge remains the same for all charges at a point
Electric potential is independent of charge
Electric potential = (Electrical potential energy) / charge
V = PEelectric / q

8. Changing Electrical Potential
Potential difference – the change in electrical potential energy associated with that charge divided by the charge of the particle
Ratio of change in electrical potential energy to charge
Symbolized by ΔV and measured in volts (V)
1V = 1J/C
Named in honor of Alessandro Volta who developed the first practical battery
Often called voltage
Small batteries typically have a potential difference of 1.5V, car batteries 12V, electrical outlets 120V

9. Changing Electrical Potential
Potential difference = -(magnitude of the electric field * displacement)
ΔV=-EΔd
Remember, we only care about displacement parallel to the direction of the electric field

10. Changing Electrical Potential
Potential difference between a point at infinity and a point near a point charge
Potential difference = Coulomb constant * (value of the point charge) / (distance to the point charge)
ΔV = kCq/r
Must have a reference point for determining electric potential
Typically assume Earth has a zero value for electric potential
Grounding – connecting an electrical device to Earth creates such a reference point

11. Changing Electrical Potential
To get the resultant potential difference for a group of charges, just add them up, keeping track of the signs
Called the superposition principle
Positive charges have positive electric potentials
Negative charges have negative electric potentials
Electric potential is a scalar so don’t have to worry about x and y components

12. Changing Electrical Potential
Batteries must do work to move charges across a potential difference
Batteries have two terminals
One positive and one negative
One positive and one grounded
Charges naturally move from positive to negative terminal in a circuit
Work must be done on the charges to move back to positive terminal
Batteries give the charge energy to move back across the potential difference