10.1 Exploring the Nature of Static Electricity

(Do Not Copy) Have you ever had your hair stand up after putting on or taking off your sweater? Why does this happen?

Atomic Structure & Electric Charge All matter is made up of atoms. Atoms contain subatomic particles

Electrons can be easily added or removed from an atom. Review According to the Bohr-Rutherford diagram: It is very difficult to remove protons & neutrons from the nucleus of an atom. Electrons can be easily added or removed from an atom.

Review If # of electrons = # of protons, then atom has NO overall charge (neutral) If # of electrons does NOT equal the # of protons, then atom has an electric charge.

Positive, Negative, & Neutral Objects Objects such as rulers, combs & airplanes have billions of positive & negative charges. Charge symbols (+ or -) will be used to represent the relative abundance and distribution of charges on an object. Each charge symbol represents a very large # of protons (+) or electrons (-). Overall charge of an object can be determined by comparing the # of protons & electrons.

Do Not Copy What is the overall charge of this object? (object C) Positive? Negative? Neutral? Why?

(Do Not Copy) Match the following terms below to diagrams a, b and c Neutral object Negatively charged object Positively charged object

Neutral object has an equal # of p & e Summary Neutral object has an equal # of p & e Negatively charged object has more e than p Positively charged object has more p than e

Charging Objects Static Electricity: - The electric charge that builds up on the surface of an object. Static electricity produces “static charges” because the charges are at rest on the surface of the object until given a path to escape

Charging Objects: When two neutral objects made of DIFFERENT materials come into contact (ex: hair & rubber balloon) both objects become charged. The balloon gains electrons & becomes negative. The hair loses electrons & becomes positive. Remember: GEN LEP (If atoms: Gain Electrons = Negative & Lose Electrons = Positive)

Friction and the Movement of Electrons This occurs when two different neutral materials are rubbed together and electric charges are moved from one object to the other One material will attract electrons and become negatively charged One material will give up electrons and become positively charged

Why do you think some materials attract electrons and some give up electrons? This is because: some atoms are more strongly attracted to electrons than others there are two different materials that are used that have different strengths on holding on to their electrons

Electron Affinity and Triboelectric Series Electron affinity is the tendency of a material/object to hold on to the electrons/gain them. As you move further down the list, the materials increase in their tendency to gain extra electrons. Why do we use this chart? To predict the charge that will be gained when two objects are rubbed together.

Lets try an example a)What will be the charge of a piece of paper after rabbit fur is rubbed on it? Answer: The paper will gain electrons from the fur and become negatively charged. Why? The rabbit fur will lose electrons to the paper and become positively charged. Why?

The Law of Attraction and Repulsion: 1. Objects that have like charges repel (-) and (-), repel (+) and (+), repel 2. Objects that have unlike charges (opposites) attract (+) and (-), attract (-) and (0), attract (+) and (0), attract

The Law of Electric Charges NOTE: A neutral object will attract a charged object (since they are unlike charges) E.g. - and neutral attract + and neutral attract Note: Neutral & neutral objects have no effect on each other (i.e. no repulsive forces or attractive forces)

A coulomb is the metric unit for electric charge COULOMB (C) COULOMBS A coulomb is the metric unit for electric charge COULOMB (C) 1 coulomb is equal to 6.24 x 1018 electrons added or removed from a neutral object

CONDUCTORS Materials that allow the movement of electrons easily E.g. Metals: Copper, silver, gold There are good and fair conductors (semiconductors) Semiconductors allow electrons to move through not as easily (water with dissolved minerals)

INSULATORS Material that does not easily allow the movement of electrons through it E.g. Non-metals: plastic, ebonite, wood, glass, PURE water Used for insulating wires in homes to protect us from the danger of having large amounts of electric charge move through our bodies if in contact

Figure b: Ceramic

Read section 10.1 – supplement your notes Homework: Read section 10.1 – supplement your notes P. 398 #1-5 P. 401 #1-5 p. 403 #2-4, 11 Read section 10.2 for next class