Ch 20 What is electrostatics The study of STATIC ELECTRICITY Static electricity is electrical charges that can be collected andor held in one place This is different from current electricity ID: 273313
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Slide1
Electrostatics
(Ch. 20)Slide2
What is electrostatics?
The study of STATIC ELECTRICITY.
Static electricity is electrical charges that can be collected and/or held in one place.
This is different from
current electricity
which is what powers your refrigerator, lights, batteries, etc.Slide3
What is charge?
Charge is divided into two categories: positive and negative
charges.
Something is said to be
charged
when it has an unequal amount of positive/negative charges.
If there are more positive charges, it is positively charged.
If there are more negative charges, it is negatively charged.
If there are the same amount, it is said to be
neutral
.Slide4
Opposites attract!
Positive charges like negative charges and will attract each other.
Similar charges (negative-negative and positive-positive) repel each other.Slide5
Where does it come from?
Electrons!
Electrons!
Electrons!
Only electrons move around from one object to another to charge objects. (Why is that?) Just like heat, electrons move from
high concentration to low concentration.Slide6
Quick!
What happens if a positively charged object
touches
a negatively charged object?
Electrons flow from negatively charged object
positive charged object until they are both neutral. Slide7
Quick!
How many electrons does something have if it is neutral?
The same amount as the number of protons!Slide8
GROUND.
In electricity the “ground” is very important. This is generally a huge body that will be electrically neutral.
The Earth is a great example of “ground.” The human body can also serve as a ground for many cases.
Example: By touching the charged object, you
ground
it.Slide9
Quick!
What happens if a negatively charged object is grounded?
What happens if a positively charged object is grounded?Slide10
How do I get some of that?!
THREE WAYS TO OBTAIN CHARGE:
Conduction (two object directly touch)
Induction (bringing a charged object near a neutral object will
induce
a charge in the neutral object).
Friction (rubbing electrons onto something)Slide11
Measure!
The SI unit for charge is the
Coulomb
. It is abbreviated with a C.
Examples:
1.0 C
3.5
μ
C
6.3
nC
The charge of 1 electron (called the
elementary
charge) is:
1.602 x 10
-19
CSlide12
Quick!
If an object has 6.022 x 10
23
more electrons than protons, what is its net charge?
6.022x10
23
electrons X 1.602x10
-19
C/electron
= 96,472 C. [that’s A LOT!!]
How many electrons are there in 1
μ
C ?
1x10
-6
C / 1.602x10
-19
C/electron
= 6.24x10
12
electrons. [that’s A LOT!!]Slide13
Conductors vs. Insulators
Conductors allow electrons to move about freely.
Metal. Graphite. Water.
Insulators do not allow electrons to move about freely.
Plastic. Rubber. Glass. Cloth. Wood.Slide14
May the force be with you.
Like charges repel. Opposites attract.
The attraction and repulsion is a
FORCE.
Electric force is a
non-contact force
.
(like gravitation!)
Electric force in an
inverse square law
.
(like gravitation!)Slide15
Coulomb’s Law
Coulomb’s law:
The force between two charges is proportional to the magnitude of the two charges and inversely proportional to the square of the distance between the two.
F = k q
1
q
2
/r
2
k is a constant = 9.0x10
9
N
•m
2
/C
2Slide16
Your turn to Practice
Please do Ch 20 Rev p 477 #s 1, 4, 7, 9, 14, 20, 21, 24-27.