Electrostatics

Electricity at the atomic level An atom is made up of a nucleus and electron orbiting. Inside the nucleus are protons (positive charged) and neutrons (no charge). Electrons orbit around the nucleus and are negatively charged.

Electrically charged atoms Qualitatively: An atom is said to be “charged” if There is an excess of electrons (the atom is negatively charged) There are more protons than electrons (the atom is positively charged)

Electrically charged atoms Quantitatively: The amount of charge an object has depends on the excess protons or electrons. The charge of an electron and the charge of a proton have the same magnitude 1.6x10-19 Coulombs

CHECK FOR UNDERSTANDING A theoretical object can have all the following charge values except 1.6x10-19 C 3.2x10-19 C 4.0x10-19 C 4.8x10-19 C 1.6x10-18 C

How to charge a neutral object Conduction: Charging by contact. Charge (electrons) can be exchanged between two objects depending on their atomic properties. Law of conservation of charge During conduction, the amount of charge to start is the same as the amount of charge after.

Materials can be split into 2 groups Some materials are ready to “give up” electrons and therefore can have electricity flow through them easily These are called conductors. Metals and water Some items are ready to “accept” electrons and therefore electricity does not flow through them easily. These are called insulators Rubber and wood

Mass and Charge of subatomic particles Give some similarities and differences between electrons, protons, and neutrons Particle Charge (C) Mass (kg) Electron -1.60x10-19 9.11x10-31 Proton +1.60x10-19 1.67x10-27 Neutron

Electrostatic Force If two charged objects are capable of attracting or repelling each other, this could cause a change in motion. Thus, charges cause a force.

Electrostatic Force What variables will effect the strength of an electrostatic force? How do they effect the strength of the force?

Coulombs Law Found by Charles Coulomb in 1790 using a torsion balance K = 9x109

Field Forces Electrostatic force is called a “field force” because it does not need contact to exist. Can you think of any other forces that act from a distance?

Newton’s Law of Gravitation Proposed by Isaac Newton in 1660’s… Look familiar??

Similarities Both a field forces relying on the inverse square of the distance the objects act on each other. Butter gun.

Differences Gravitational force is ONLY attractive Electric force can be attractive or repulsive. Electric force is usually much stronger! Proton and electron of a hydrogen atom example again…

Example The electron and proton of a hydrogen atom are separated, on average, by a distance of about 5.3x10-11 m. Find the magnitude of the electric force that each particle exerts on the other.

Given:

The force is negative, which means in this case, that the electric force is attractive.

Same example again… What about the force of gravitational attraction between the electron and proton?

Givens

Much, much, much smaller gravitational force compared to electrostatic force