Coulombs Law Electric Force Two positively charged spheres

Coulomb’s Law

Electric Force ] Two positively charged spheres will repel each other. ] The force will cause a q deflection until equilibrium is reached. q 1 m, q 2 r ] The apparatus can measure the properties of electric force.

Inverse Square ] Closer spheres exhibit more electric force. ] The electric force decreases as q the square of the distance. q 1 m, q 2 r ] This is an inverse square force. • Compare to the force of universal gravitation

Total Charge ] Increasing the charge of either sphere increases the total force. • Linear increase with either charge q ] The force is proportional to the q 1 m, q 2 r product of the two charges.

Coulomb’s Law ] The force also depends on the material separating the charges. • • • Simplest material is a vacuum Expressed as a constant k = 8. 99 x 109 N m 2 / C 2 Permittivity of free space: e 0 = 1/4 pk ] The formula is known as Coulomb’s Law. • The sign of the charges indicates attraction or repulsion

Vector Force ] The electric force is a vector. q 1 ] The force acts in a line q 2 between two charges. ] The force one charge is equal and opposite to the force acting on the other charge of a pair. ] Multiple charges add their forces as vectors. q 3 q 1 q 2

Electricity vs. Gravity ] A hydrogen atom consists of ] From Coulomb’s law: an electron and proton at an average distance of r = 0. 53 x 10 -10 m. ] Find the relative forces due to ] From Newton’s Gravitation: electric charge and gravity between the particles. ] Useful facts: • qe = qp = 1. 6 x 10 -19 C • me = 9. 1 x 10 -31 kg • mp = 1. 67 x 10 -26 kg ] The ratio is: next