Chapter 20 Static Electricity Electrostatics - The study of electrical charges that can be collected and held in one place.

Chapter 20 Static Electricity ChargeSize ProtonPositive1.67 x kg ElectronNegative9.11 x kg NeutronNeutral1.67 x kg

Chapter 20 Static Electricity Every atom is composed of a positively charged nucleus, around which are distributed a number of negatively charged electrons. Electrons of all atoms are the same. Each has the same quantity of negative charge and the same mass. Protons and neutrons compose the nucleus. Protons are 2000 times more massive than an electron and carry an equal amount of charge. All normal atoms have equal number of protons and electrons.

Chapter 20 Static Electricity

Charged versus Uncharged Objects Positively-Charged Possesses more protons than electrons Negatively-Charged Possesses more electrons than protons Uncharged Equal numbers of protons and electrons

Chapter 20 Static Electricity Electric Charge: Positive or negative Charge is quantified Like charges repel, opposites attract Charges exert a force through a distance. The force is stronger when the charges are close together

Chapter 20 Static Electricity

Grounding Connecting a charged object to earth to remove an object’s charge. Conductor Any material through which an electric charge is readily transferred. Insulator Any material through which an electric charge is not readily transferred. Induction The process of charging an object by bringing it into the electric field of another object.

Chapter 20 Static Electricity

- + Charge by Conduction

Chapter 20 Static Electricity Charge by Induction

Chapter 20 Static Electricity

Coulomb The quantity of electric charge 1 coulomb = 6.25 x electrons 1 electron = 1.6 x coulombs

Chapter 20 Static Electricity Coulomb’s Law The force between two charged objects vary directly with the product of their charges and inversely as the square of the distances between them. F force (N) q charge (C) k 9 x 10 9 N m 2 / C 2 Inverse Square Law

Chapter 20 Static Electricity q 1 = 1 x C q 2 = -5 x C D =.5 m k = 9 x 10 9 N m 2 / C 2 Find the force of attraction between charges of 100 µC and -50 µC separated by a distance of 50 cm.

Chapter 20 Static Electricity Find the force of attraction between charges of 100 µC and -50 µC separated by a distance of 50 cm. F = -180 N The negative means a force of attraction

Chapter 20 Static Electricity q 1 = 5 x C q 2 = 3 x C D =.04 m k = 9 x 10 9 N m 2 / C 2 Two charges are separated by 4.0 cm. Object A has a charge of +5 µC and object B has a charge of +3 µC. What is the force on object A?

Chapter 20 Static Electricity Two charges are separated by 4.0 cm. Object A has a charge of +5 µC and object B has a charge of +3 µC. What is the force on object A? F = 84 N The positive means a force of repulsion

Chapter 20 Static Electricity A positive charge of 3.5 x C has 2 charges nearby. One has a negative charge of -1.2 x C and is.03 m away at 180°. The second charge is a positive charge of 3 x C at 270° at.02 m. What is the total force on the 3.5 x C charge?

Chapter 20 Static Electricity m.02 m + F2F2 F1F1

Chapter 20 Static Electricity + F2F2 F1F1 F 1 = 42 N F 2 = 236 N

Chapter 20 Static Electricity F 1 = 42 N + F 2 = 236 N F 2 = (42 N) 2 + (236 N) 2 = F F = 240 N tan  = 42 N/236 N =.178  = 10° The force on the 3.5 x C is 240 N at 100º

Chapter 20 Static Electricity A negative charge of 4.5 µ C has 2 charges nearby. One has a negative charge of 1.2 µ C and is.04 m away at 90°. The second charge is a negative charge of 2.1µ C at 180° at.03 m. What is the total force on the 4.5 µ C charge?

Chapter 20 Static Electricity m.04 m - F2F2 F1F1

Chapter 20 Static Electricity F 2 = 30 N F 1 = 95 N - F2F2 F1F1

Chapter 20 Static Electricity F 2 = (30 N) 2 + (95 N) 2 = 9736 F = 99 N tan  = 30 N/ 95 N =.315  = 17° The force on the 4.5 µC is 99 N at 343º - 30 N 95 N φ