1. Unit 5: Electricity Chapter 14: Electric Charges and Forces
14.1 Electric Charge and Current
14.2 Electric Current, Resistance, and Voltage
14.3 Capacitors

2. SWBAT… describe how charges are transferred.
Objective Date 3/9/15
SWBAT… describe how charges are transferred.

3. Electric charge
Electric charge, like mass, is also fundamental property of matter.
Inside atoms found in matter, attraction between positive and negative charges holds the atoms together.
The unit of charge is the coulomb (C). 1

4. Electric charge and current
The direction of current was historically defined as the direction that positive charges move.
Benjamin Franklin first used the terms “positive” and “negative” to describe charge. 2

5. Conventional current
Because of Franklin’s work, the direction of electric current is defined as going from positive to negative.
Long after Franklin’s work, scientists discovered that current in wires is the flow of electrons which move in a circuit from negative to positive.
3 & 4

6. Electric Charge Objects can lose or gain electric charges.
The net charge is also sometimes called excess charge because a charged object has an excess of either positive or negative charges.
A tiny imbalance in either positive or negative charge on an object is the cause of static electricity. 5

7. Electrostatics
Electrostatics is the part of physics that studies the forces created by unmoving charges.
A photocopier uses electrostatic forces.

8. Electric forces
The forces between the two kinds of charge can be observed with an electroscope. 6
An electroscope contains two very thin leaves of metal that can swing from a central rod connected to a metal ball. Charges can flow freely between the ball and the leaves.
Suppose a positively charged rod touches the metal ball of an electroscope.
Some negative electrons are attracted to the rod.
The metal ball and leaves of the electroscope are left with a net positive charge.
Since both leaves have the same positive charge, the leaves repel each other and spread apart.
Once an electroscope is charged, it can be used to test other charged objects.
The leaves spread farther apart if another positively charged rod is brought near the metal ball.
This happens because the positive rod attracts some negative electrons from the leaves toward the ball, increasing the positive charge on the leaves. 8

9. Charging by friction
Under dry conditions, a balloon rubbed on hair will transfer electrons from hair to the balloon.
This is called charging by friction.
Objects charged by this method will attract each other.
Once the balloon is charged, it can also stick to a neutral wall through “polarization”

10. Charging by induction
Charging by induction is a method of using one object to charge another without changing the net charge on the first object. 7

11. Conductor: Electrons in random motion
If a copper wire is not connected to a battery, the free electrons move around at high speeds.
They have no net motion because as many move one way as the other way.

12. Conductors and insulators
A semiconductor has a few free electrons and atoms with bound electrons that act as insulators. 8

13. Capacitors A capacitor is a storage device for electric charge.
Capacitors can be connected in series or parallel in circuits, just like resistors. 9

14. Capacitors
A capacitor can be charged by connecting it to a battery or any other source of current.
A capacitor can be discharged by connecting it to any closed circuit that allows current to flow.

15. Capacitance Capacitance is measured in farads (F).
A one-farad capacitor can store one coulomb of charge when the voltage across its plates is one volt.
One farad is a large amount of capacitance, so the microfarad (μF) is frequently used in place of the farad.

16. Introductory Electrostatics Notes Name:
3 Sub-Atomic Particles in the Atom:
___________ which have _____________ charge.
KEY
Electrons negative
Protons positive
Neutrons no
Electric Forces
Opposite charges ________________ each other.
Like charges ____________ each other.
The closer the charges are together, the _________ the force.
The further the charges are together, the __________ the force.
attract
repel
stronger
weaker

17. electrons protons fussion electrons protons fission
Introductory Electrostatics Notes Name:
KEY
Charging Atoms
An atom can have a Positive charge by …
SUBTRACTING ___________________
ADDING ________________ (also called nuclear ___________)
An atom can have a Negative charge by …
ADDING _________________
SUBTRACTING _____________ (also called nuclear _______________________________)
electrons
protons
fussion
electrons
protons
fission