1. Pick up a copy of the notes from the front Think about this question and be ready to answer if called on… – How are gravity and electrostatic force similar? How are they different?

2. Electrostatics Just the basics

3. Static Electricity STATIC ELECTRICITY- ELECTRICAL CHARGES THAT DO NOT MOVE A. ELECTRICAL CHARGES 1. AN OBJECT IS NEUTRAL IF IT HAS EQUAL NUMBERS OF POSITIVE (PROTONS) AND NEGATIVE (ELECTRONS) CHARGES. 2. AN OBJECT IS ELECTRICALLY NEGATIVE WHEN IT HAS MORE ELECTRONS THAN PROTONS. 3. AN OBJECT IS ELECTRICALLY POSITIVE WHEN IT HAS MORE PROTONS THAN ELECTRONS.

4. Static Electricity B. IF TWO NEUTRAL OBJECTS ARE RUBBED TOGETHER THEY CAN BECOME CHARGED. 1. ONLY ELECTRONS ARE TRANSFERRED - PROTONS DO NOT MOVE. C. MATERIALS THROUGH WHICH CHARGES WILL NOT MOVE EASILY ARE CALLED ELECTRICAL INSULATORS. D. MATERIALS LIKE METALS THROUGH WHICH CHARGES WILL MOVE EASILY ARE CALLED ELECTRICAL CONDUCTORS. A. METALS ARE GOOD CONDUCTORS BECAUSE AT LEAST ONE ELECTRON ON EACH ATOM OF THE METAL CAN BE REMOVED EASILY.

5. Static Electricity LIGHTENING - WHEN ELECTRICAL CHARGES BUILD UP ENOUGH IN A CLOUD OR ON THE GROUND DURING A STORM, AIR BECOMES A CONDUCTOR. 1. THESE CHARGES ARE STRONG ENOUGH TO REMOVE ELECTRONS FROM MOLECULES IN THE AIR. 2. THESE CHARGED AIR MOLECULES BECOME FREE TO MOVE. THEY FORM A CONDUCTOR THAT IS PLASMA.

6. Charging Objects A. HENREY CAVENDISH (1760) DID EXPERIMENTS WITH CHARGED METAL RODS. B. CAVENDISH CONCLUDED THE FOLLOWING: 1. THERE ARE TWO CHARGES - POSITIVE AND NEGATIVE 2. CHARGES EXERT FORCE ON OTHER CHARGES OVER A DISTANCE. 3. THE FORCE IS STRONGER WHEN THE CHARGES ARE CLOSER TOGETHER. A). THIS FOLLOWS AN INVERSE SQUARE LAW VERY SIMILAR TO THE LAW OF GRAVITATION. 4. LIKE CHARGES REPEL, UNLIKE CHARGES ATTRACT

7. Charging Objects ELECTROSCOPES ARE DEVICES USED TO DETECT ELECTRICAL CHARGES. 1. UNCHARGED ELECTROSCOPE - LEAVES HANG STRAIGHT DOWN. 2. WHEN A CHARGED OBJECT TOUCHES THE ELECTROSCOPE, THE ELECTRONS MOVE DOWN THROUGH THE METAL LEAVES. A) BECAUSE THEY ARE LIKE CHARGES THE LEAVES REPEL EACH OTHER. (AND SPREAD APART)

8. Charging Objects D. CHARGING BY FRICTION - WHEN OBJECT COME IN CONTACT WITH EACH OTHER, ONE OBJECT MAY RUB OFF ELECTRONS FROM THE OTHER OBJECT. E. CHARGING BY CONDUCTION - CHARGING A NEUTRAL OBJECT BY TOUCHING IT WITH A CHARGED BODY. SUCH AS IN AN ELECTROSCOPE AS DEMONSTRATED PREVIOUSLY. F. CHARGING BY INDUCTION - USING CHARGE SEPARATION TO CHARGE AN OBJECT. 1. CHARGING A NEUTRAL OBJECT BY BRINGING A CHARGED BODY NEAR IT, WITHOUT TOUCHING IT.

9. Millikan’s Oil Drop Experiment A. FINE OIL DROPS WERE SPAYED INTO A CONTAINER WITH TWO CHARGED PLATES. B. DROPS WERE ALLOWED TO FALL THROUGH A SMALL HOLE ONE AT A TIME. C. THE DROPS (NEGATIVE IN CHARGE) WERE HELD IN SUSPENSION AS THE POTENTIAL DIFFERENCE BETWEEN THE PLATES WAS ADJUSTED. THE TOP PLATE WAS POSITIVE.

10. Millikan’s Oil Drop Experiment FROM HIS EXPERIMENT, HE DISCOVERED THE VALUE OF THE CHARGE FOR AN ELECTRON: q e = 1.60 x 10 -19 C Oil source

11. Coulomb’s Law A. CHARGES PUSH AND PULL ON EACH OTHER. THE PUSH OR PULL IS A FORCE. 1. THIS FORCE DEPENDS ON THE SIZE OF THE CHARGES AND THE DISTANCE BETWEEN THEM. B. THE SYMBOL FOR CHARGE IS q. THIS IS BECAUSE IT WAS ONCE ALWAYS REFERED TO AS THE QUANTITY OF CHARGE.

12. Coulomb’s Law C. IN 1785, CHARLES COULOMB DISCOVERED THE RELATIONSHIP BETWEEN FORCE, CHARGES, AND DISTANCE BETWEEN THE CHARGES (SEPARATION). THE EQUATION IS AS FOLLOWS: F =K (q a q b ) d 2 F = force (newtons) (N), q = charge (coulombs) (C), d = distance between charges (m), K = is a constant that equals 9.0 x 10 9 Nm/C2

13. Practice Problem Two charges are separated by 3.0 cm. Object A has a charge of +6.0 C while object B has a charge of +3.0 C. What is the force on object A?

14. Voltage (ALSO KNOWN AS POTENTIAL DIFFERENCE) A. VOLTAGE IS THE PUSH OF ELECTRONS. 1. IT IS THE MEASURE OF ENERGY AVAILABLE TO MOVE ELECTRONS. 2. THE HIGHER THE VOLTAGE, THE MORE ENERGY EACH ELECTRON CARRIES, AND THE MORE WORK IT CAN DO. B. MEASURED IN UNITS CALLED VOLTS (V).

15. The end… …For today