Electric Fields

Force over a distance Both gravity and electric force act over a distance without touching (unlike other forces) Very difficult for early scientists to accept Michael Faraday proposed the Electric Field to explain

Electric Field Force that extends outward from any charged object and permeates through space Any second charged object placed around the first charge will feel a force of attraction or repulsion due to this field Tested with an imaginary positive test charge (q)

Magnitude of the force acting on the test charge can be measured

Definition Electric field (E) is defined as the amount of force (F) per unit of charge (q) E = F/ q units N/C

Another Equation E = F/ q F = k qQ/ r2 E = k Q/ r2

Example Find the magnitude and direction of the electric field on a particle P which is located 30 cm right of a point charge of –3.0 x 10-6 C.

If the field is due to more than one charge, the total field is the sum of the two individuals

Example Find the total field acting on point P. If P is a proton initially at rest, what will its acceleration be? 20 cm 25 cm P Q1 = -25μC Q2 = +50μC

Field Lines Lines of force can be drawn to visualize the force acting on a single point charge Stronger fields have more lines On point charges On double points Start on + and go to - On plates

Fields and Conductors The electric field inside any good conductor is zero - charge distributes itself evenly over the surface of a conductor making the net field inside zero Electric field is always perpendicular to the surface of a conductor Excess charge tends to accumulate on sharp points or areas of greatest curvature

What will happen? +