Electrostatics

The Atom All matter is composed of atoms that contain: Protons (positively charged particles) Neutrons (neutrally charge particles) Electrons (negatively charged particles) Every atom has a positively charged nucleus surrounded by negatively charged electrons.

Electric charge, “q”, is measured in Coulombs, C. All electrons are identical in mass and quantity of charge : q = x C All protons are identical to other protons and although they are more massive than electrons, they have the same quantity of positive charge as electrons have negative charge: q = x C Compare the mass difference!

Electrical forces explain bonding in molecules. All neutrons are identical to other neutrons, have more mass than protons, and have neither positive or negative charge. Atoms typically have the same number of protons as electrons so the atom has a net charge of zero. When an atom has lost or gained electrons, it is charged and called an ION.

Charles Coulomb, mid 1700’s, studied and published papers about the electrostatic force between 2 charged objects.

The fundamental rule of electricity: Like charges repel; opposites attract. A neutral object will attract both positive and negative charges

Ben Franklin was the first to use the terms “positive” and “negative” to describe electrical charge. Mid 1700’s Hmmm

Coulomb’s Law calculates the electrical force between charges: where k is a constant, k = 9 x 10 9 N·m 2 /C 2

Sample problem using the formula sample problem Physics Classroom website

Sample Problems using logic The electrostatic force between two charges located 2 meters apart is 0.10 N. What will the force between these charges when they are located 1 meter apart? Solution: The distance has halved. The force will become stronger if the charges are closer. To get the factor, put ½ in place of d in the denominator (remember to square it). F ≈ 1/d 2 1/( 1/2) 2 = 1/(1/4) = 4; now multiply the original force times the factor  (.10)(4) =.40N

A 2-C charge and a 4-C charge attract each other with 10 N of force. How much will a 2-C charge and an 8-C charge attract each other when placed the same distance apart? Solution: one of the charges doubled. The force will be stronger since force and charge are directly related. The force will double: 10 N X 2 = 20 N

The charge on an electron is 1.6 x C. How many electrons make a charge of 4.0C? Set up a proportion!! 1 e - = ??? e -

Number of electrons, e - I want to know how many electrons are in a lightning bolt that transfers 20 Coulombs of charge. I know the number of Coulombs for 1 e – is equal to 1.6 X C. I can set up a proportion, cross- multiply and divide. 1 e – =? e – 20 X 1 / 1.6 X X C20 C= 1.25 X That’s a lot of electrons!!!

Conductors have easily moveable electric charges Many are metals that have “free electrons” Positive ions may also be mobile Insulators Charges cannot move easily Examples: plastic, wood, glass u8l1d.cfm

Semiconductor -Conductivity is between conductors and insulators unlike metals, they can conduct more efficiently with temperature increase used in computers Superconductor: NO resistance to the flow of electrons. So far, no material is a superconductor except at extremely low temperatures.

– Water: insulator or conductor? PURE water does NOT conduct electricity Bath water (or water from the tap) often has impurities or ions that allow conduction The purer the water, the lower the conductivity (the conduction of electricity is called ELECTROLYTIC behavior- ) – Air: insulator or conductor? Usually an insulator, thankfully When strong forces are present, electron’s can be stripped from air molecules, creating ions example: lightning

Lightning An electrical discharge between the clouds and the ground or between two clouds. Ions in the air react to form high heat plasma, producing an expansion: a flash we see as lightning and the boom we hear as thunder!!