1. Current Or Moving Right Along Standards:
5a Students know how to predict the voltage or current in simple direct currrent (DC) electronic circuits constructed of batteries, wires, resistors , wires and capacitors.
5b Students know how to solve problems involving Ohm’s Law.
5c Students know that any resistive element in a DC circuit dissipates energy, which heats the resistor. Students can calculate the power (rate of energy dissipation) in any resistive circuit element using the formula P=I I R.

2. Electric Current Variables
Definition
Units
Water analogy
Current (I)
Movement of electric charge (I=Q/t)
Coulombs / second or amperes (A)
Water that flows in pipe
Voltage Drop or Potential Difference
(DV )
Electrical pressure
Joules/coulomb or Volts (V)
Difference in heights of pipe ends
Resistance (R)
Objects ability to oppose current
Ohms (W)
Rocks in pipe or width of pipe
Question: Define the terms current, voltage difference and resistance. What units are used to measure each? Are these vector or scalar quantities?
Activities:
State that last week we dealt with electric charge that stayed on an object perhaps after being transferred. Today we will deal with charges that move.
Define current as moving electric charge measured in coulombs per second or Amperes. Mathematically I= Q/t where Q is the amount of charge that moves past a point in time interval and t is the time interval.
Define voltage difference as electrical pressure or energy difference. This is an energy variable. Remind students that the 2nd law of thermodynamics states that things tend to move from high to low potential energy. Thus charge will move from higher to lower voltages. In other words there must be a difference of potential and voltage for charge to move. Measured in Joules / Coulomb or volts. A scalar quantity.
Define resistance and the resistance of a material to electric flow. Measured in ohms which is the resistance a wire has if a 1 volt drop results in 1 amp of current.
Discuss water analogy

3. Check Question
Which of the following is a flow of charge and which is the cause of that flow?
Current is the flow and voltage difference is the cause of the flow
Voltage difference is the flow and current is the cause of the flow
Current is the flow and resistance is the cause of the flow

4. Ohm’s Law DV I x R Current = voltage difference / resistance
I has direct linear relationship with DV
I has inverse linear relationship with R
True as long as resistance does not change much with temperature DV
I x R
Question: State Ohm’s law. How are current and resistance related? How are current and voltage drop related? Under what conditions is Ohm’s law true?
Remind students of yesterdays lab and ask what was relationship between voltage drop and current? How about the length of the wire oand current? Do longer wires have more or less resistance? And thus what is the relationship between resistance and current. Write I~voltage drop and I ~ 1/resistance and then combine to make Ohms law.
State that law is true as long as resistance of material does not change much with temperature.

5. Power Law
Electrical power or power dissipated is a measure of how fast electrical energy is changed into another energy
Resistor changes PEE into heat
Light bulb changes PEE into light and heat
Motor changes PEE into kinetic energy
P = IDV = I2R = DV2 / R
Measured in Joules/ second or watts P
I x DV P
I2 x R
Question: What energy transformations do a resistor, light bulb and motor make? Write the three equations used for calculating electric power.
Activites:
Define electrical power as the rate at which electrical energy is converted into another form of energy. It is measured in Joules / second or watts and is a scalar quantity. Definitional equation is Power = energy transformed / time for transformation.
Talk about energy transformations different electronic devices make: resistor electric energy to heat, light bulb=> electrical energy to light and heat, motor=> electrical energy to kinetic energy, capacitor=> electrical energy to electric field potential energy
Write power equations and show how first becomes second becomes third using Ohm’s law.
Introduce and demonstrate Power circles. Derive using Ohm’s law if have time.
DV2
P x R

6. Check Question Current Voltage Difference Resistance Power 20 V
10 ohms
3 A
5 ohms
20 A
100 W

7. Resistance of a Wire Direct relationship with length
More length=>more atoms=>more collisions
Inverse relationship with thickness
More space for charge to spread out => less collisions
Direct relationship with temperature
Higher temperature=>higher speeds=>more collisions
Resistor
Voltage drops, current remains constant
Changes electrical energy into thermal energy
How does the resistance of a wire vary with the following: a) length b) thickness c) temperature? Does a resistor change the voltage, current or both that flows through it?
Activities:
Remind students of yesterday’s labs and write conclusions: resistance increases with length, decreases with diameter.
Add that for most materials resistance increases with temperature.
Show students several examples of resistors.

8. Check Question
Which of the following wires will have the highest resistance?
A) Short and thick
B) Long and thick
C) Long and thin
D) Long and thick

9. Current Carrying Wire
Must have voltage difference for charges to move (current)
Charges contained in wire (battery provides energy to move charges not charges themselves)
Charges move relatively slowly (1 cm/hr) while energy that moves charges moves at nearly speed of light
Overall charge of wire remains zero whether charges move or not
Conventional current assumes direction of positive charges I
Question: What is required for current to occur in a wire? What is the charge of a current carrying wire? How do the speeds of the charges in a wire compare to the speed that the energy is transferred between the charges? What is a conventional current?
Activities:
Draw wire with charges in it. Ask if charges exert force on one another and whether force is attractive or repulsive. For this reason charges essentially march thru wire in step keeping constant distances between them. Draw legs on charges and colonel voltage yellling March.
Point out that for the above reason the number of charges in the wire never changes. If one charge goes in, one comes out. In other words the charge of a current carrying wire is zero.
Also point out that a battery need not supply charges for the wire. They are already in the wire.
Ask how fast do the charges move. Remind students that there are other atoms in wire that charge will bump into. This makes there motion rather slow. For an electron starting at the negative side of a battery to go all the way through the car it takes about 6 days. That’s a speed of 1 cm/hr.
If the above is so then why does a light turn on when you flick a switch. First remember the charges are already throughout the wire. Second realize that the voltage drop or electrical field moves through the wire at nearly the speed of light in a vacuum. Thus all charges hear the march order at the same time and get moving fairly quickly.
Finally, state that it is indeed the electrons that move through a current carrying wire. But due to Benjamin Franklin wrongly guessing that it was the positive charge that moved, we have a whole set of rules that assume positive charge flow. It turns out that you get the same numerical answers either way but the directions are opposite. So we often use what is called a conventional current which is in the direction that positive charge would flow.

10. Check Question
Why can a bird stand on a single 6000 V power line and not be electrocuted?
Bird has high resistance
Voltage not large enough
Both legs feel the same voltage so no voltage drop

11. AC/DC
Charges move first one way then opposite direction (they alternate direction)
Use same electrons over and over again.
Produced by generators, wall current is example
Charges move one direction only
Use different electrons over time
Produced by batteries and solar cells
Question: How do AC and DC differ? How are they the same? What are the sources of each?
Activities:
1) Time will be short so project slide and read through it as students write it down.

12. Check Question
Which of the following is more dangerous (could start a fire)?
Plugging a 120 V microwave into a 220 V electrical outlet
Plugging a 220 V dryer into a 120 V electrical outlet
Both are dangerous