Créer une présentation
Télécharger la présentation

Télécharger la présentation
## AP Physics III.A

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**AP Physics III.A**Electrostatics**The Fundamental Charge (Robert Millikan and his oil drop**experiment)**Ex. How many electrons are in two Coulombs of negative**charge?**Law of Conservation of Charge – during any one process,**net electrical charge of an isolated system remains constant.**Ex. Two identical isolated conducting spheres, one with**charge -6 μC and another with net charge +2 μC are allowed to touch. If the two spheres have the same net charge after touching, what is the net charge on each sphere?**18.4 Charging by Induction and Conduction (also known as,**“I wish I had a decent electroscope”)**Ex. An electron “orbits” the proton of a hydrogen atom**at an average distance of 0.53 EE 10-10 m. What is the force that the proton exerts on the electron? What is the velocity of the electron for a circular orbit?**Ex. Two charges exert electrical force F on each other. If**the magnitude of each charge is doubled and the distance between them is halved, what is the force F′ on each charge in terms of F?**p. 552: 3-5, 7, 11, 15, 19, 21, 23, 79B7**• 3.4 EE -17 kg, mA > mB 79B7 • FBD b)**Charges experience an electrostatic force due to the**presence of other charges**Force per Coulomb is the definition of an electric field**(“show me the formula”)**An electric field is a vector that has a direction that the**force exerts on a positive test charge.**Ex. Find the electric force on a proton placed in an**electric field of 2.0 EE 4 N/C that is directed along the positive x-axis.**Electric fields are vectors. The net electric field at a**point in space can be determined by considering the contributions of each charged object and adding them together as vectors.**Ex. Electric Field Between Two Point Charges. Two point**charges are separated by a distance of 0.100 m. One has a charge of –25.0 μC and the other 50.0 μC. a) What is the magnitude and direction of the electric field at point P between them 0.020 m from the negative charge? b) If an electron is placed at rest at P, what is the magnitude and direction of its initial acceleration?**p. 553: 25, 29, 31, 35-37; 81B3**• a) 182 N/C b) 312 N/C 81B3 • FBD b) E = 5800 N/C, FT = 0.058 N c) drawing**Electric potential decreases or increases not because the**field exerts any more or less force (the field is uniform – like gravity near the Earth’s surface). V changes because of distance. A charge released in the field, traveling a greater distance converts more of its Ue to K (like dropping an object from a greater height).**Potential (and therefore potential difference) is scalar**(this will simplify some things).**Summary**• Electric potential energy – energy a charge has because of its potential in an electric field (so far the field is uniform) • Electric potential – electric potential energy per unit charge • Potential difference – change in electric potential**Another formula and an hilarious story about twin boll**weevils.