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* J –Results from interaction of two objects’ charges –Is a form of mechanical energy ME = KE trans + KE rot + PE g + PE elastic + PE electric

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) PE electric = -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 + charge- charge In same direction of electric field Loses PE electric Gains PE electric In opposite direction of electric field Gains PE electric Loses PE electric

Electrical Energy and Electric Force Electrical potential energy for a pair of charges Electrical potential energy = Coulomb constant * charge 1 * charge 2 / distance PE electric = k C q 1 q 2 /r k C = 8.99*10 9 N*m 2 /C 2 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.