# Phy Lecture Essay

1070 Words5 Pages
Example - A Lot of Electrons How many electrons are there in one coulomb of negative charge? Adding or removing electrons from matter will acquire an electric charge with magnitude equal to e times the number of electrons added or removed, N. N= q "1.00 C = = 6.25 # 1018 -19 e -1.60 # 10 C q = Ne e = "1.60 # 10 "19 C coulombs ! ! Question A brass key has a net positive charge of +1.92 ! 10-16 C. Approximately, how many electrons must be added to the key to make it electrically neutral? a) 770 b) 960 c) 1200 d) 1800 e) 2100 18.1.1. • Conductors and Insulators 18.3 Conductors and Insulators Conductors and Insulators Question Which one of the following statements concerning electrical conductors is false? a) A material that is a good electrical conductor has many free electrons that can easily move around inside the material. Not only can electric charge exist on an object, but it can also move through an object. Substances that readily conduct electric charge are called electrical conductors. Materials that conduct electric charge poorly are called electrical insulators. b) When a positively-charged object is moved into contact with an electrical conductor, electrons move toward the object. c) Rubber is an excellent electrical conductor. d) Materials that are good thermal conductors are often good electrical conductors. e) Most metals are very good electrical conductors. 18.3.2. 18.2 Charging Objects Transferring Charges by Rubbing One Object with Another • Charging Objects The body that loses electrons has an excess of positive charge, while the body that gains electrons has an excess of negative charge. LAW OF CONSERVATION OF ELECTRIC CHARGE During any charge transfer the total electric charge of an system remains constant. (Charge is conserved). 18.4 Charging by Contact Question Complete the following