Electrostatics

1
Electrostatics


-
-
-

2
Conservation of Charge
Charge can neither be created nor destroyed
Positive ions ---- fewer electrons than protons
Negative ions ---- fewer protons than electrons
Electric Charge is measured in Coulombs 6.3x1018
electrons make -1.0 C of charge 6.3x1018 protons
make 1.0 C of charge
3
Conservation of Charge
Charge can neither be created nor destroyed
rub electrons from a bar with fur bar becomes
positively charge by the exact amount
that fur becomes negatively charged.
bar becomes a tiny bit less massive
4
Coulombs Law
The interaction force between two charges is
directly proportional to the size of each charge
(q1 and q2) and inversely proportional to the
square of their separation distance (d) k 9.0 x
109 N/m2/C2
FegtgtgtFg
5
Coulombs Law
The interaction force between two charges is
directly proportional to the size of each charge
(q1 and q2) Double either q1 or q2 then F
doubles. Double both then F quadruples
6
Coulombs Law
The interaction force between two charges
is inversely proportional to the square of their
separation distance (d) Double the separation
distance then F is reduced to (1/4) Halve the
separation distance then F is quadrupled (4x)
7
Coulombs Law
The interaction force between two charges
is inversely proportional to the square of their
separation distance (d) triple the separation
distance then F is reduced to (1/9) (1/3) the
speration distance then F is increased 9 fold (9x)
8
Coulombs Law
The interaction force between two charges
is inversely proportional to the square of their
separation distance (d) If separation distance
is increased by 10 then F (Reduces/increases) by
_________________
9
Coulombs Law


As the charges above are released the force on
each (increases or decreases)
10
Coulombs Law


As the charges above are released the speed of
each (increases or decreases)
11
Coulombs Law


As the charges above are released the
acceleration of each (increases or decreases)
12
Coulombs Law
?

As the charges above are released the speed of
each increases. Thus the green object has a
__________ charge. Positive, negative, cant
tell
13
Coulombs Law
?

As the charges above are released the force on
each increases. Thus the green object has a
__________ charge. Positive, negative, cant
tell
14
Conductors
Conductors have very loosely bound electrons.
That is electrons that are not really attached to
one particular nucleus. These electrons are
sometimes called free electrons because they move
freely when exposed to an electric
field Gold Copper Silver Ionic solutions (salt
water)
15
Insulators
Insulators have very tightly bound electrons.
That is electrons that are firmly attached to one
particular nucleus. These electrons are very
hard to set in motion throughout the
material Glass Dry wood Plastic
16
Semiconductors
Semiconductors have moderately bound electrons.
These electrons can be set into motion throughout
the material when a moderately strong electric
field is established in the material. Carbon Sil
icon
17
(No Transcript)
18
(No Transcript)
19
Superconductors
Superconductors have no electrical resistance to
charge flow (infinite electrical
conductivity) Very cold silver (-269 C)
20
Charging
Friction Contact Induction
21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
Charge Polarization
-
- -
- -
- -
- -
-
- -
- -
- -
- -
- -
- -
- -
- -
-
-
F
25
Electric Field
EF/q

q

26
Electric Field
EF/q
-

q
27
Electric Field
EF/q or Fq E

- - - - - -
F

q
Uniform Electric Field between two charged plates
28
Electric Shielding E0 inside metals
29
Electric Shielding E0 inside metals

- - - - - -
30
Electric Potential (Volts)

- - - - - -
Electric Potential energy (J) Charge
(C)
F
EP EPE / q VoltJoule/Coulomb

q
Electric Potential Energy Work Electric
Potential Energy Charge x Volts 1 Joule
Coulomb x Volt
31
(No Transcript)
32
Physical science 101 stop here
33
Electric Potential (Volts)

- - - - - -
Electric Potential energy (J) Charge
(C)
F

q
What is the electric potential between two
plates when it takes 2.0 J of work to move a
0.001 C charge from - to plate?
34
What is the electric potential between two plates
when it takes 2.0 J of work to move a 0.001
Ccharge from - to plate?
Given WEPE2.0 J Charge0.001 C Want
EP Solution Electric Potential
Electric Potential energy (J) Charge
(C)
35
Given WEPE2.0 J Charge0.001 C Want
EP Solution Electric Potential
Electric Potential energy (J) Charge
(C) 2.0 J/0.001 C 2000 Volts 1 Volt1J/C
36
Capacitors Energy Storage

- - - - - -
F

q