Transcript Coulomb`s Law

Electric Charge
and
Electric Field
Write at least three
questions that you have
about ELECTRICITY.
Questions
What causes electricity?
Why is electricity harmful? How much is
lethal?
What is the difference between static
electricity and current electricity?
What makes electrons move?
What is the difference between an amp and
a volt?
What makes a conductor conductive?
Questions
1. T or F, Electric charges behave just like
magnets in that they only repel each
other.
Vocabulary
Electrostatics
Electric Charge
Neutral
Insulator
Conductor
Charging by induction
Law of conservation of
charge
Coulomb’s law
Elementary charge
Electrons
Permittivity of free
space
Principle of
superposition
Electric field
Reading
Chapter 16, Electric Charge and Electric Fields
Electrostatics
Study of electrical charges collected and
held in one place
Examples
Static electricity from the clothes dryer
Static electricity from combing your hair
Where does charge come from?
Conductors and Insulators
Elementary Charge
One electron has a charge of
1.602 x 10 -19 Coulombs
One coulomb is the charge on 6.25 x 10^18
electrons
A large lightning bolt is about 10 coulombs
Conservation of Charge
CHARGE
Can be transferred
Cannot be created or destroyed
Electric Charge
Like charges repel. Opposite charges attract.
Separation of Charge
An electroscope can be used to detect the presence and relative amount.
Charging by Induction
Coulomb’s Law
Coulomb’s Law
•Used to calculate the magnitude of electric force
•Inverse square law
Click image to view movie.
Similarities Between Coulomb’s Law and Newton’s
Law of Universal Gravitation
Inverse Square Laws
Forces on Charges
Coulomb’s Law
Two balloon’s are located 15 cm apart. Each
balloon holds a charge of +6.0 μC.
Calculate the electrostatic force is exerted by
each balloon.
Superposition of Forces- Find force
on charge A
Example Problem: Determining the Total
Force Exerted on the Positive Charge
Electric Fields
How can you tell that Earth has a
Gravitational Field?
Electric Field
a region around a charged object where the object’s
electric force is exerted on other charged objects.
Electric Field
• The strength of an electric field is equal to the
force on a positive test charge divided by the
strength of the test charge.
• The direction of an electric field is the direction
of the force on a positive test charge.
• A test charge always must be small enough so
that its effect on “Q” is negligible.
• The magnitude of the electric field strength is
measured in Newtons per coulomb, N/C.
Example Problem- Electric Field
A positive test charge of 3.0 x 10-6 C experiences a force of
0.12 N at an angle of 15º north of east. What are the
magnitude and direction of the electric field at the
location of the test charge.
Drawing Electric Fields
An electric field is a region around a charged object where the
object’s electric force is exerted on other charged objects.
Electric Fields
Additional Resources
Use Electricity and Magnetism CD
Use www.falstad.com
Quiz- Draw the Electric Field
1. A positive charge
2. A negative charge
3. One positive and one negative charge of equal
magnitude
4. Two positive charges of equal magnitude
5. Two negative charges of equal magnitude
6. One positive and one negative charge of unequal
magnitude
7. Two positive charges of unequal magnitude
8. Two parallel plates with opposite charges
Superposition of E-fields
E = E 1 + E 2 + E3
E = F/q = F1/q +F2/q +F3/q
Van de Graaff Generator
Homework
Physics: Principles and Problems, Glencoe
Electric Charge
Chapter 20, p558-559, #23-28, 30, 34-36, 41-43, 49, 51
Electric Field
Chapter 21, p.585-587, #67, 71, 73, 74
AP Physics
Additional Slides
JJ Thompson’s Experiment
Rutherford’s Gold Foil
Experiment
Transferring Charge
There are three methods by which
charges can be transferred to build
up static electricity: charging by
friction, by conduction, and by
induction.
Electric Force
An electric field is a region around a charged object where the
object’s electric force is exerted on other charged objects.
Lightning
Click the Video button to watch a movie about lightning.
Electric Force
An electric field is a region around a charged object where the
object’s electric force is exerted on other charged objects.