Slides and Homework for Electricity Unit
Electrostatics
Electrostatics
You will get a charge out of these shocking factoids...
•
•
•
•
There are only two kinds of charge.
Ben Franklin defined them.
Charge is conserved.
Charge is quantized.
lel = 1.60219E­19 C
1 Coulomb of charge = 6.3E18 electrons
k qq
m
m
G
Fg = 2 Fe = 2
R
R
Field
Fe
E =
Fe = E q
It's like W=mg where g is gravitational field strength
q
kq
E
=
Field has units of N/C
R2
Fe = E q
You will get a charge out of these questions...
1. A combination of four electrons and two protons would have a net charge of...
a) +2
b) ­2
c) +3.2 E­19 Coulombs
d) ­3.2 E­19 Coulombs
2. A vulcanite rod is stroked with cat fur on a frosty night and then held securely. An electron is then placed 1 cm above the rod. Sketch a free body diagram of the forces acting on the electron. 3. How would your free body diagram change if the electron was replaced by a proton?
Fe is opposite direction (downward) and Fg is greater b/c protons are 200 times more massive than electrons.
4. a) If a neutral solid object becomes positively charged, does its mass increase or decrease?
b) How about if it becomes negatively charged? 5. a) If two objects are seen to electrically repel each other, can you be certain that they are both charged?
b) How about if they are seen to attract? No, one or the other object may be neutral
YES
6. List the steps involved in charging a pith ball by induction...
7. A proton and an electron are placed 1 m apart in an otherwise empty universe. a) What is the gravitational attraction between them?
1.03E­67 N
At least my
hair is more bitchin!
b) What is the electrical attraction between them? 2.3E­28 N
1,000,000,000,000,000,000,000,000,000,000
Times Stronger Than Gravity!!!!!!
E
6 μC
4 μC
• In an elevated position, the ram has gravitational potential energy. When released, this energy is transferred to the pile below. • Similar energy transfer occurs for electric charges.
ELECTRODYNAMICS http://www.wired.com/thisdayintech/2010/02/gallery­lightn
100 Lightning strikes per second...thats 8.6E6 per day!
This sums it up nicely...
Politically correct ethnic mix.
Current and Resistance
More Current and Resistance
Resistance
1.
V=IR
...words are weak!
2.
V=IR
3. 4.
Ω
Draw the symbol used for the unit Ohms...______
7.
5.
8.
6.
9.
10.
11.
12.
13.
14.
15.
That's Gross
Watts Up With Electrical Power?
But...
So...
Current
16.
False
17.
Duh
18.
True
Provides a path (ground) for excess charge to flow through so it won't flow through you!
Brought to you by...
Duh
A simple Circuit:
A circuit that is made up of only batteries and resistors.
"Tools" Needed to Analyze Simple Circuits
• Ohm's Law
• The Equations for Power
• Kirchhoff's Rules
• Rules for Finding Equivalent Resistance
Kirchhoff's Junction Rule
The sum of the currents flowing into, and out of, a junction
in a circuit must be equal. (conservation of matter/charge)
Kirchhoff's Loop Rule
The sum of the potential changes around any closed circuit loop is zero.
(Conservation of energy)
Schematic Diagrams
Series Circuit
Parallel Circuit
R
R
R
9V
Combining Resistors in Compound Circuits
Series
Parallel
Circuit Training Part 1
#1 Simplify This...(find the equivalent resistance)
#2 Simplify This...
#3 Simplify This...
#4. Find the Total Current in Circuit #3.
use V=IReq
#5. Find the Current through the 10 Ω resistors in Circuit #3.
Voltage across the branch containing the 10 Ω
resistors is 60 volts, Ohms law predicts the current through them I=60V/20Ω. *Note that I
used the equivalent resistance of the branch.
Circuit Training Part 2
Example 1
Example 2
Example 3
Example 4
1.
2.
3.
4.
5.
6.
7.