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Chapter 20 Static Electricity. Electrostatics - The study of electrical charges that can be collected and held in one place. Chapter 20 Static Electricity. Chapter 20 Static Electricity.
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Chapter 20 Static Electricity • Electrostatics - The study of electrical charges that can be collected and held in one place.
Chapter 20Static 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 20Static 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 20Static 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 20Static 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 20Static Electricity Charge by Conduction
+ + + - + + + + + + + Chapter 20Static Electricity Charge by Induction
Chapter 20Static Electricity Coulomb The quantity of electric charge 1 coulomb = 6.25 x 1018 electrons 1 electron = 1.6 x 10-19 coulombs
Chapter 20Static 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 109 N •m2/ C2 Inverse Square Law
Chapter 20Static Electricity Find the force of attraction between charges of 100 µC and -50 µC separated by a distance of 50 cm. q1 = 1 x 10-4 C q2 = -5 x 10-5 C D = .5 m k = 9 x 109 N •m2/ C2
Chapter 20Static 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 20Static 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? q1 = 5 x 10-6 C q2 = 3 x 10-6 C D = .04 m k = 9 x 109 N •m2/ C2
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 20Static Electricity A positive charge of 3.5 x 10-6 C has 2 charges nearby. One has a negative charge of -1.2 x 10-6 C and is .03 m away at 180°. The second charge is a positive charge of 3 x 10-6 C at 270° at .02 m. What is the total force on the 3.5 x 10-6 C charge?
F2 .03 m + + - F1 .02 m + Chapter 20Static Electricity
F2 + F1 Chapter 20Static Electricity F1 = 42 N F2 = 236 N
F F2 = 236 N + F1 = 42 N Chapter 20Static Electricity F2 = (42 N)2+ (236 N)2 = 57460 F = 240 N tan = 42 N/236 N = .178 = 10° The force on the 3.5 x 10-6C is 240 N at 100º
Chapter 20Static Electricity A negative charge of 4.5 µ C has 2 charges nearby. One has a negative charge of 1.2 µC and is .04 m away at 90°. The second charge is a negative charge of 2.1µC at 180° at .03 m. What is the total force on the 4.5 µC charge?
- .04 m .03 m F1 - - - F2 Chapter 20Static Electricity
F1 - F2 Chapter 20Static Electricity F1 = 95 N F2 = 30 N
Chapter 20Static Electricity 95 N F2 = (30 N)2+ (95 N)2 = 9736 - φ F = 99 N 30 N tan = 30 N/ 95 N = .315 = 17° The force on the 4.5 µC is 99 N at 343º