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Electric Charge and Electric Field

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Presentation on theme: "Electric Charge and Electric Field"— Presentation transcript:

1 Electric Charge and Electric Field
AP Physics Chapter 16

2 Electric Charge and Electric Field
16.1 Static Electricity

3 Static electricity – not moving Two types of charge
positive (+) when electrons are lost negative (-) when electrons are gained Objects can gain charges by rubbing 16.1

4 Unlike charges attract
16.1 Static Electricity Like charges repel Unlike charges attract Law of Conservation of electric charge – the net amount of electric charge produced in a process is zero 16.1

5 Electric Charge and Electric Field
16.2 Electric Charge in the Atom

6 16.2 Electric Charge in the Atom
Atoms are made of positive protons negative electrons Electrons move from one object to another when the objects are rubbed Eventually charges bleed off objects because water molecules are polar 16.2

7 Electric Charge and Electric Field
16.3 Insulators and Conductors

8 16.3 Insulators and Conductors
Conductors – outer electrons of atoms are free to move through the material Insulator – electrons tightly held, do not move 16.3

9 16.3 Insulators and Conductors
Semiconductors – conduct electricity under some circumstances, don’t under other conditions 16.3

10 Electric Charge and Electric Field
16.4 Induced Charge; the Electroscope

11 16.4 Induced Charge; the Electroscope
Induction – charging without contact Object is brought near a charged object Electrons move Object is grounded An electroscope measures if an object has a charge on it 16.4

12 Electric Charge and Electric Field
16.5 Coulomb’s Law

13 Electric charges apply forces to each other From experiments
16.5 Coulomb’s Law Electric charges apply forces to each other From experiments Force is proportional to charge Inversely proportional to square of distance 16.5

14 Equation – gives magnitude of force
16.5 Coulomb’s Law Equation – gives magnitude of force Opposite charges – force directed toward each other Like charges – force directed away from each other Charge is measured in Coulombs 16.5

15 Charges are quantized – that is they come in discrete values
16.5 Coulomb’s Law 1 Coulomb is the amount of charge, that if placed 1 m apart would result in a force of 9x109 N Charges are quantized – that is they come in discrete values The constant k relates to the constant called the permittivity of free space 16.5

16 We will assume that charges are point charges - size is negligible
16.5 Coulomb’s Law AP tends to write k as We will assume that charges are point charges - size is negligible 16.5

17 Electric Charge and Electric Field
16.6 Solving Problems Involving Coulomb’s Laws and Vectors

18 16.6 Coulomb’s Law and Vectors
Principle of Superposition – Electrostatic forces are added just like any other force As vectors 16.6

19 Electric Charge and Electric Field
16.7 The Electric Field

20 Electrical forces act over distances Field forces, like gravity
16.7 The Electric Field Electrical forces act over distances Field forces, like gravity Michael Faraday electric field – extends outward from every charge and permeates all of space The field is defined by the force it applies to a test charge placed in the field 16.7

21 The Electric field would then be Or q is the test charge
We can also say that Remember that E is independent of the test charge. The electric field is also a vector (free body diagrams are probably a good idea) 16.7

22 Electric Charge and Electric Field
16.8 Field Lines

23 To visualize electric fields Draw electric field lines
Direction of the lines is the direction of force on a positive test charge The density of the lines indicates relative strength of the field Note: the field density increase as you get closer 16.8

24 For multiple charges, keep in mind
16.8 Field Lines For multiple charges, keep in mind Field lines indicate the direction of the field The actual field is tangent to the field lines The magnitude of the field is relative to the field line density Fields start at positive and end at negatives Field Lines 16.8

25 If the field is produced by two closely spaced parallel plates
16.8 Field Lines If the field is produced by two closely spaced parallel plates The field density is constant So the electric field is constant 16.8

26 Electric Charge and Electric Field
16.9 Electric Fields and Conductors

27 16.9 Electric Fields and Conductors
For a conductor The electric field inside a conductor is zero (static) Any net charge is distributed on the surface of a conductor Electric field is always perpendicular to the surface of a conductor Charges concentrate at the area of greatest curvature 16.9


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