ELECTRICITY----STATIC AND CURRENT 31,
2012
Objectives:
Describe how charged objects interact by using the law of electric charges.
Describe one way in which an object can become charged.
Do Now: What are the parts of an atom? Do you know?
Homework: Energy Project Due tomorrow!!! Make sure you email it to me by class tomorrow or it will be late!

Chapter 17
Section 1 Electric Charge and
Static Electricity

• Like charges repel; Opposite charges attract

Chapter 17
Section 1 Electric Charge and
Static Electricity
Electric Charge

Electricity is the energy caused by the flow of electrons.
 Charges Exert Force Atoms are composed of particles with electric charge.
 The law of electric charges states that like charges repel and opposite charges attract.

Chapter 17
Section 1 Electric Charge and
Static Electricity
Electric Charge, continued
 The Force Between Protons and Electrons
Because protons and electrons have opposite charges, they are attracted to each other.
 The Electric Force and the Electric Field The force between charged objects is an electric force.
 An electric field is the region around a charged object in which an electric force is exerted on another charged object.

Do Now: Using the Law of Electric Charges, predict
+
A B C
_
1. Between A & B?
2. Between B & C?
3. Between A & C?
• Objective: define static electricity and describe the
3 ways an object can become charged!
• Homework: Go to Mrs. Anicito’s page and open the lightning assignment. Complete for Thursday!

Charge and Static Electricity

Chapter 17
Static Electricity : A BUILD UP
OF CHARGE (electrons) on an object!
 Electric Discharge: loss of static electricity
 Detecting Charge You can use a device called an electroscope to see if something is charged.

Chapter 17
Charge It!
Electric Charge and Static
Electricity
 Friction Charging by friction happens when electrons are “wiped” from one object onto another.
 Conduction Charging by conduction happens when electrons move from one object to another by direct contact.
 Induction Charging by induction happens when charges in an uncharged metal object are rearranged without direct contact with a charged object.

1. Friction: build up of charge by rubbing one object against another.
Rubbing hair with balloon

2. Conduction : build up of charge by direct contact between 2 objects

3. Induction: build up of charge by force of attraction or repulsion WITHOUT touching one object to the other ( through open space )
Demo with Salt

FRICTION (f)
Use the word bank to select your BEST answer.
INDUCTION (i) CONDUCTION (c)
1._____Electrons transferred from one object to another by direct contact.
2.____ Charges on an object rearrange without direct contact when a charged object is near it.
3. ____Rub 2 objects together. The electrons are transferred.
4. ____Rub a balloon on a wool sweater, and place it near a wall.
5. ____ Walking across a carpet.

Write the letter that most applies for each word
.
1.___ Repel A. Objects with opposite charges come together.
2.___ Electroscope B. Detects charges.
3.___ Attract C. Objects with like charges jump apart.
Answer the questions.
State the Law of Electric Charges:
_______________________________________
____________________________________
List the three ways in which an object can become charged:
5) 6) 7)

When an object becomes charged, one object ________ electrons, and one object _______ electrons.
multiple choice:
_____ Electric force is found between a) Charged objects b) credit cards c) criminals
_____ The area around a charged particle that can exert a force is called : a) electric force b) electric shock c) electric field
11. ______ The build up of electric charges on an object is a) current electricity b) static electricity c ) electric discharge

E. True /False. CORRECT the False!!
17.____ A lightning bolt is an example of electric discharge.
18.____ An electroscope can tell if the charge is pos. or neg.
19.____ Static electricity is NOT as noticeable in the summer because of the dryness in the air.
20._____ Lightning is a result of the negative charges in the clouds being attracted to the negative charges on the ground.

http:// phet.colorado.edu/en/simulation/ballo ons2011 electricity.ppt

• http://player.discoveryeducation.com/index.cf
m?guidAssetId=5AE05296-1087-4C59-A5B9-
4585869125DC&blnFromSearch=1&productco de=US

• Current is a flow of electric charges. It is not a build up of charge that is discharged.
• All current elec. needs a circuit—a pathway for electric charges to flow..
• All circuits must have at least 3 parts :
1) wires, 2) a source and 3) a load(s).

Load wires
Source of electricity

• Conductor: a material that easily allows the
flow of electric charges.
• It gives very little resistance to the flow of charge. ( metals – copper, aluminum , etc )

• Insulators: do not easily allow for the flow of electric charges through them.
• Ex: glass, plastic, certain rubber materials, cloth.

• http://www.brainpop.com/technology/energy technology/currentelectricity/

• http://www.brainpop.com/science/energy/ele ctriccircuits/ http://www.brainpop.com/scienc e/energy/electriccircuits/

• Like Charges repel; Unlike charges attract.

• 1. Series Circuit: only 1 path for the electric charges to flow
• 2. Parallel Circuit: has More than one path for the electric charges to flow.

Series circuit

• This is what “slows down” the movement of the electric charges … so they hit each other more…
• What do you think could ADD resistance in a circuit ?
• Add more loads to the same circuit
• Heat
• Longer wires
• Thinner wires

• Take a sheet of computer paper.
• You have 4 drawings, 4 circuits to build, and 4 questions to answer… Let’s do the drawings together, then you can build, and answer the questions:
• You Label: wires, source, load, direction, terminals, switch
• 1. 3.
• 2. 4.

2. Parallel Circuit: has more than 1 path for electric charges to flow, so if 1 load goes “out,” the other loads will still work !

http:// phet.colorado.edu/en/simulation/circu it-construction-kit-dc

• Electric charges move back and forth—homes and buildings.
Ex: 60 V one way and 60 V the other way,= 120 Volts

• 2 types circuits 2 types current direction
1 way
Series
Direct current
Parallel
Alternating current
Direct with a battery
Back and forth
One way

BATTERIES
CONVERT CHEM.
ENERGY TO
ELECTRICITY.
2 TYPES:
A)DRY CELLS
B)WET CELLS
Dry cells have paste-
like electrolytes, and these are the batteries you are used to using.
Wet cells have liquid
electrolytes. ( car batteries)
•
• Electrolytes- liquids/acids that cause a chem. reaction, that releases electric charges
Batteries (usually) are DC-
direct current- where the electrons flow only in 1 direction.

dry cell
Wet cell

Watch the stick figures move the charges
Back and forth, creating a potential difference
In voltage, making current !
http://phet.colorado.edu/en/simulation/batte ryvoltage http://phet.colorado.edu/en/simulati on/battery-voltage

Plug fuses Circuit breaker-open a circuit to keep from Overload.
• Circuit breaker fuses

CURRENT
SYMBOL
:
I
UNITS: Amperes
WHAT IS IT?
The # of electrons. the rate at which charges pass a given point
More electrons=more current; less electrons = less current
RESISTANCE
R or
OHM’S
The opposition to the flow of electrons; High resistance has more opposition to the flow
4 THINGS THAT AFFECT R:

Thin/thick wires

Temperature

Length Wire

Type of wire-
Copper-good conductor; decrease R; Iron- poor conductor; increase R
↓ Thickness = ↑ R
↑ Temperature =↑ R
↑ Length = ↑ R
VOLTAGE
V
Volts
The energy of each electron.
Low voltage = little energy.
High Voltage =
High energy

Ohm’s law
I = V/ R

•What current would flow through a resistor of 20 ohms connected to a 12 V supply?
• [A] 240 A • [B] 1.66 A • [C] 0.67 A • [D] 0.067A
What current would flow through a resistor of 40 ohms connected to a 10 V supply?
• [A] 400 A • [B] 4 A • [C] 0.25 A • [D] 0.025A
A 100 ohm resistor is connected to a 20 V supply. What current flows?
• [A] 0.02 A • [B] 0.05 A • [C] 0.2 A • [D] 0.5 A • [E] 2000 A
What value of resistor would be used to permit a current of 0.2
A to flow using a 6V supply?
• [A] 0.03 ohms • [B] 0.3 ohms • [C] 3.0 ohms • [D] 30 ohms •
[E] 300 ohms