Download ELECTRODYNAMICS

ELECTRODYNAMICS http://www.wired.com/thisdayintech/2010/02/gallery­light
100 Lightning strikes per second...thats 8.6E6 per day!
Current and Resistance
I = ΔQ
Δt
Sorry again for that whole
positive/negative fail.
I
"Conventional Current" tracks the flow of positive charges in a circuit.
Andre­Marie Ampere
1 Ampere = 1
Call me Marie and I'll
kill you!
Voltage Sources: Maintain a potential difference between the ends of a conductor (wire) and cause the flow of electrons (a current). They act like a charge pump that lifts charge to a higher potential.
+
­
Symbol
Plug in the toaster and the wires get hot. Why?
YOUR RESISTANCE IS FUTILE
Slam Dancing
resistance­in­a­wire_en.jar
Useful Analogy: Wire resistance is like sucking a liquid through a straw...
"thickness" or viscosity of liquid
Length of straw
size of hole
Ask me to tell you the wire story.
http://www.snopes.com/business/genius/wire.asp
The Secret Code Painted on Carbon Resistors
naturally...there's an app for that
Ohm my
legs are bowed
My Cousin Charles Brown
ohms­law_en.jar
GEORG
OHM
Example: Semiconductors like silicon.
This sums it up nicely...
Politically correct ethnic mix.
More Current and Resistance
Resistance
1.
V=IR
...words are weak!
2.
V=IR
3. 4.
Draw the symbol used for the unit Ohms...______
Ω
7.
5.
8.
6.
9.
10.
11.
12.
13.
14.
15.
That's Gross
Current
16.
False
17.
Duh
18.
True
Provides a path (ground) for excess charge to flow through so it won't flow through you!
Watts Up With Electrical Power?
But...
So...
The next part of this unit is 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
• Haywood
Gustav Kirchhoff
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)
Recall that voltage is like elevation. The batteries "lift" the charges
up to a higher potential. The resistors drop the potential.
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.
Fuses
Circuit Breakers
Circuit Training Part 3
1. a.) Draw a schematic diagram for a circuit that has a 9 V battery and three 10 Ω resistors connected in series with a parallel branch containing 3 more 10 Ω resistors.
b.) Label the direction of the "conventional current" through the battery.
c.) Determine the magnitude of the current through the battery.
2.
What is the current through the battery?
10 Ω
100 V
5 Ω
8 Ω
10 Ω
12 Ω
20 Ω
10 Ω
2 Ω
6 Ω
3.
a.) What is the current through the 12 Ω resistor in circuit #2?
b.) What is the current through the 6 Ω resistor in circuit #2?
a.) The same as the current through the Battery...2.08 A
b.) First find the voltage drop across the parallel branch then apply Ohms law...
4. Watt power rating does the light bulb have?
See watt I did there?
10 Ω
120 V
10 Ω
12 Ω
20 Ω
6 Ω
5 Ω
10 Ω
8 Ω
50 Ω
2 Ω
5.
a.) At a rate of $0.10 per kilowatt­hour how much would it cost to run the light for the 3 weeks until the final exam?
b.) With that same amount of energy, how many apples could you lift a distance of one meter?
Attachments
resistance­in­a­wire_en.jar
ohms­law_en.jar