1. Electrostatics

2. Electric Charge The source of negative charge is the electron The source of positive charge is the proton The smallest possible amount of charge, the elementary charge, is 1.6 x 10 -19 Coulombs Electron charge = - 1.6 x 10 -19 C Proton charge = + 1.6 x 10 -19 C – All other amounts of charge are multiples of these Electric Charge is a conserved quantity

3. What is an Electric Field? One charged object can influence another charged object without any direct contact. We say a charged object is surrounded by an electric field, a region of influence. Any other charged object in that space will interact with that field and experience an electrical force.

4. Electric Field Strength The electric field strength at a given location is defined as the amount of force per unit of charge at that location. E = F / q (units of E: N/C) This is analogous to the way we described gravitational field strength earlier in the year: g = F g /m

5. Field around a positive charge A positive charge placed in this field will feel a force directed away from the source of the field…repulsion A negative charge placed in this field will feel a force directed towards the source of the field…attraction

6. Field around a negative charge A positive charge placed in this field will feel a force directed toward the source of the field…attraction A negative charge placed in this field will feel a force directed away from the source of the field…repulsion

7. Field around two opposite charges (same amount) Any charge placed in the field will feel a force in a direction tangent to the field lines

8. Field around two like charges (same amount)

9. Electric Field Lines When drawing, or interpreting, electric field lines keep in mind the following… – Filed lines originate at + charge or infinity – Field lines terminate at – charge or infinity – Filed lines are always perpendicular to the surface of a charged object – Line density is an indicator of field strength – The number of lines leaving a + and terminating at a – is proportional to the magnitude of charge – Field lines NEVER cross each other (Why?)

10. Electric Force – how strong is it?

11. Determine the electrostatic force on the electron in a hydrogen atom from the proton in the nucleus Q 1 = Q 2 = r = For comparison purposes, determine the gravitational force between them as well…