Electrostatics: Electric Charges, Forces, and Potential - Prof. Jicong Shi, Study notes of Physics

Download Electrostatics: Electric Charges, Forces, and Potential - Prof. Jicong Shi and more Study notes Physics in PDF only on Docsity! Summary of Chapter 16 & 17 • There are two kind of electric charges, positive and negative. The total charges is conserved. Like charges repel and opposite charges attract. • The magnitude of the force between two charges is F = k Q1Q2 r2 The net force from several charges is the vector sum of all the forces between each pair ~F = ~F1 + ~F2 + ~F3 + ... • The magnitude of the electric field ~E is at any point in space is the electric force per unit charge and the direction of ~E is the direction of the electric force on a positive charge at that point: ~E = ~F q If there are multiple charges in space, the total electric field due to all charges is the vector sum of the electric field due to each individual charge, ~E = ~E1 + ~E2 + ~E3 + ... where ~Ei is the electric field due to charge i. Under the electric force, an initially rested positive charge will move in the direction of ~E and an initially rested negative charge will move in the opposite direction of ~E. Field lines indicate the direction of the field, field lines start on positive charges and end on negative charges. The electric force on a positive charge is in the same direction of the field line and the force on a negative charge is in the opposite direction of the field line. • Electric Potential V : The electric potential energy of a charge q inside electric field is PE = qV where q > 0 for a positive charge and q < 0 for a negative charge. The electric potential is higher at the upstream of the field lines and lower at the downstream of the field lines. Under the electric force, an initially rested positive charge moves from higher V to lower V and an initially rested negative charge moves from lower V to higher V . The change of the electric potential energy when a charge moves from point a to point b is PEb − PEa = q(Vb − Va) 1