Transcript Electrical Potential Energy

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