Transcript ELECTRICITY----STATIC AND CURRENT

Electric Charge and Static Electricity
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
Law of Electric Charges
• 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.
What is happening in these pictures?
March 5, 2013
Do Now: Using the Law of Electric Charges, predict
what
– will happen: 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
Electric Charge and Static
Electricity
Charge It!
 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.
Static electricity by friction
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
Study Jams - Electricity
3 Ways to Charge an Object
Use the word bank to select your BEST answer.
FRICTION (f)
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
2.___ Electroscope
3.___ Attract
A. Objects with opposite charges
come together.
B. Detects charges.
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
discharge
b) static electricity
c ) electric
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
Lightning video
• http://player.discoveryeducation.com/index.cf
m?guidAssetId=5AE05296-1087-4C59-A5B94585869125DC&blnFromSearch=1&productco
de=US
Current electricity
• 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).
Parts of a circuit
wires
Load
Source of electricity
Conductors
• 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
• Insulators: do not easily allow for the flow of
electric charges through them.
• Ex: glass, plastic, certain rubber materials,
cloth.
Current electricity– brain pop
http://www.brainpop.com/technology/e
nergytechnology/currentelectricity/
• http://www.brainpop.com/technology/energy
technology/currentelectricity/
Types of circuits
• http://www.brainpop.com/science/energy/ele
ctriccircuits/http://www.brainpop.com/scienc
e/energy/electriccircuits/
Law of electric Charges
• Like Charges repel; Unlike charges attract.
2 main types of circuits
• 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
Now, let’s draw it in your notes:
Resistance
• 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
Circuit Mini Lab
• 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 !
Draw a parallel circuit
Circuit simulation
http://phet.colorado.edu/en/simulation/circu
it-construction-kit-dc
Alternating Current - AC
• Electric charges move back and forth—homes
and buildings.
Ex: 60 V one way and 60 V the other way,= 120 Volts
Let’s recap:
• 2 types circuits 2 types current direction
Series
Direct current
1 way
Parallel
Alternating current
Back and forth
Direct with a battery
One way
BATTERIES
CONVERT CHEM.
ENERGY TO
ELECTRICITY.
2 TYPES:
A)DRY CELLS
B)WET CELLS
Dry cells have pastelike 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 DCdirect current- where the
electrons flow only in 1
direction.
dry cell
Wet cell
Inside a dry cell
Inside a 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
ryvoltagehttp://phet.colorado.edu/en/simulati
on/battery-voltage
Circuit breakers and fuses
Circuit breaker-open a circuit to keep
from Overload.
Plug fuses
• Circuit breaker
fuses
CURRENT
RESISTANCE
VOLTAGE
V
SYMBOL: I
UNITS: Amperes
R or
OHM’S
WHAT IS IT?
The # of electrons. the rate
at which charges pass a
given point
The opposition to the
flow of electrons; High
resistance has more
opposition to the flow
The energy of each
electron.
Temperature
Length Wire
Type of wireCopper-good conductor;
decrease R; Iron- poor
conductor; increase R
energy
Volts
Low voltage = little
energy.
4 THINGS THAT AFFECT R:
High Voltage = High
Thin/thick wires
More electrons=more ↓ Thickness = ↑ R
current;
↑ Temperature =↑ R
less electrons = less
↑ Length = ↑ R
current
Ohm’s law
I = V/ R
Current = voltage/ resistance.
•Discuss wires and resistance!!
•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