Download presentation
1
Electrostatics
2
10.1 Properties of Electric Charges
3
10.1 Properties of Electric Charges
Static electricity – not moving Two types of charge positive (+) when electrons are lost negative (-) when electrons are gained Objects can gain charges by rubbing 10.1 Properties of Electric Charges
4
10.1 Properties of Electric Charges
Like charges repel Unlike charges attract Law of Conservation of electric charge – the net amount of electric charge produced in a process is zero 10.1 Properties of Electric Charges
5
10.1 Properties of Electric Charges
Robert Millikan – charge is always a multiple of a fundamental unit Quantized – occurs in discrete bundles The discrete bundle is an electron The charge on a single electron is 10.1 Properties of Electric Charges
6
10.2 Insulators and Conductors
7
10.2 Insulators and Conductors
Conductors – outer electrons of atoms are free to move through the material Insulator – electrons tightly held, do not move 10.2 Insulators and Conductors
8
10.2 Insulators and Conductors
Semiconductors – conduct electricity under some circumstances, don’t under other conditions Charges can be transferred by contact Called Charging by Conduction 10.2 Insulators and Conductors
9
10.2 Insulators and Conductors
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 10.2 Insulators and Conductors
10
10.3 Coulomb’s Law
11
Electric charges apply forces to each other
From experiments Force is proportional to charge Inversely proportional to square of distance 10.3 Coulomb’s Law
12
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 10.3 Coulomb’s Law
13
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 10.3 Coulomb’s Law
14
These are forces, so be sure to use vector math, draw free body diagrams
For multiple objects, require multiple free body diagram 10.3 Coulomb’s Law
15
10.4 The Electric Field
16
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 10.4 The Electric Field
17
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) 10.4 The Electric Field
18
10.5 Electric Field Lines
19
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 10.5 Electric Field Lines
20
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 10.5 Electric Field Lines
21
If the field is produced by two closely spaced parallel plates
The field density is constant So the electric field is constant Electric Diple – two point charges of equal magnitude but oppsite sign 10.5 Electric Field Lines
22
10.6 Conductors in Electrostatic Equilibrium
23
10.6 Conductors in Electrostatic Equilibrium
Electrostatic Equilibrium – when no net motion of charge occurs within a conductor The electric field is zero everywhere inside a conductor Any excess charge is on the surface of a conductor 10.6 Conductors in Electrostatic Equilibrium
24
10.6 Conductors in Electrostatic Equilibrium
The electric field just outside a charged conductor is perpendicular to the conductors surface 4. The charge accumulates on areas of greatest curvature 10.6 Conductors in Electrostatic Equilibrium
25
10.7 Potential Difference and Electric Potential
26
10.7 Potential Difference and Electric Potential
Electricity can be viewed in terms of energy The electrostatic force is conservative because it depends on displacement Now We can calculate this value for a uniform electric field 10.7 Potential Difference and Electric Potential
27
10.7 Potential Difference and Electric Potential
Positive test charge – increases when moved against the field Negative test charge – increases when moved with the field Electric Potential (Potential) – electric potential energy per unit charge 10.7 Potential Difference and Electric Potential
28
10.7 Potential Difference and Electric Potential
Only difference in potential are meaningful Potential Difference (Electric Potential Difference) – is measureable Measured in volts (after Alessandro Volta) 10.7 Potential Difference and Electric Potential
29
10.7 Potential Difference and Electric Potential
If we want a specific potential value at a point, we must pick a zero point. That point is usually either A. The ground B. At an infinite distance 10.7 Potential Difference and Electric Potential
30
10.8 Electric Potential & Potential Energy
31
10.8 Electric Potential & Potential Energy
Using calculus it can be shown that the electric potential a distance r from a single point charge q is Assuming that potential is zero at infinity Like Potential Difference, this value is a scalar So 10.8 Electric Potential & Potential Energy
32
10.9 Potentials and Charged Conductors
33
10.9 Potentials and Charged Conductors
All points on the surface of a charged conductor in electrostatic equilibrium are at the same potential. The electric potential is a constant everywhere on the surface of a charged conductor in equilibrium. The electric potential is constant everywhere inside a conductor and equal to its value at the surface. 10.9 Potentials and Charged Conductors
34
10.10 Capacitance
35
Capacitor – device that stores electric charge
In RAM, Camera Flash, 10.10 Capacitance
36
Simple capacitors consist of
two plate The symbol for a capacitor is The symbol for a cell is The symbol for a battery is 10.10 Capacitance
37
This process takes a short amount of time
When a potential difference is placed across a capacitor it becomes charged This process takes a short amount of time The charge on each plate is the same, but opposite charge The amount of charge is proportional to the potential difference A constant C (Capacitance) gives Charging a Capacitor Time for RC Circuit 10.10 Capacitance
38
Capacitance – Unit Farad
For a parallel plate capacitor, the capacitance depends on the area of the plates, the distance between the plates 10.10 Capacitance
39
10.11 Combinations of Capacitors
40
10.11 Combinations of Capacitors
Parallel – more than one pathway For a parallel set of capacitors – the total charge is the sum of the individual charges In all parallel circuits – the potential across each branch is the same as the total 10.11 Combinations of Capacitors
41
10.11 Combinations of Capacitors
The equivalent capacitance is the value of one capacitor that could replace all those in the circuit with no change in charge or potential Since And We combine and get 10.11 Combinations of Capacitors
42
10.11 Combinations of Capacitors
Series – components of a circuit are in one pathway The magnitude of the charges is the same on each plate 10.11 Combinations of Capacitors
43
10.11 Combinations of Capacitors
The total potential is the sum of the potential drops across each capacitor We then use that equation and the equation for capacitance We get 10.11 Combinations of Capacitors
44
10.12 Energy Stored in a Charged Capacitor
45
10.12 Energy Stored in a Charged Capacitor
Capacitors store energy Energy can be defined as change in work Or the are under a plot of Q vs. V 10.12 Energy Stored in a Charged Capacitor
46
10.13 Capacitors with Dielectrics
47
10.13 Capacitors with Dielectrics
Most capacitors have an insulator between the plates Called a Dielectric Increases the capacitance by a factor K Called the dielectric constant 10.13 Capacitors with Dielectrics
48
10.13 Capacitors with Dielectrics
Some Dielectric Constants Material K Paper 3.7 Glass 5 Rubber 6.7 Mica 7 Strontium Titanate 300 10.13 Capacitors with Dielectrics
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.