Introduction:

Circuits produce a conductive path through which free electrons can continuously move.  Just like the flow of a liquid through a garden hose, this continuous movement of free electrons through the conductors of a circuit is called a current (I). Voltage (V) is the force motivating electrons to "flow" in a circuit. Voltage is a measurement of the potential energy that is always relative between two points such as the positive and negative electrodes of a battery. When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point.  Free electrons tend to move through conductors with some degree of friction. This opposition to motion is called resistance (R). The amount of current in a circuit depends on the amount of voltage available to move the electrons, and the amount of resistance in the circuit. Just like voltage, resistance is a quantity relative between two points.  Resistance is measured in units called Ohms, voltage in volts (V), and current in amperes (A).  The formula used to calculate resistance is R=V/I.

Wire can be made from any conductor.  Metals are good conductors of heat and electricity.  So which metal should be used for conducting electricity?  In lab today you will research the densities of copper, aluminum, silver, and gold.  All of these metals are capable of conducting heat and electricity.  You are to find which one is the best conductor for the most reasonable price.
 

Which metals are better conductors and why?
 

If a metal has a higher density, then it will be a ..... conductor of electricity.  If a metal has a low resistance, then is will be a .... conductor of electricity.
 

Part 1

(1) 10 cm length of copper wire
(1) 10 cm length of aluminum wire
(1) 10 cm length of iron wire
(3) brass push pins
(1) hot glue gun
(1) glue stick
(1) candle
(1) book matches
(1) stop watch
(1) beaker tongs
(1) pair goggles

Part 2

(2) D cells
(1) double D cell holder
(1) light bulb
(1) light bulb holder
(1) 10 cm length of copper wire
(3) 5 cm lengths of copper wire
(1) 5 cm length of aluminum wire
(1) 5 cm length of  iron wire
(1) ammeter
(1) voltmeter

Part 3

apparatus from Part two (batteries, ammeter, voltmeter and wires)
(1) 5 cm copper wire
(1) 25 cm copper wire


(1) 50 cm copper wire
(1) 10 cm copper wire 0.20 mm in diameter
(1) 10 cm copper wire 0.56 mm in diameter
(1) 10 cm copper wire 0.71 mm in diameter

Part 1  (Conductivity of Different Metals)
Hold all three lengths of wire in your hand .  Grab all of them firmly and twist them together 5 cm from the top.  You will end up with what looks like a wire fan. See below.

Put some hot glue on each of the three brass push pins and glue them to the free end of each wire type. Let them cool.

Construct a data table (spreadsheet) in Excel to record the type of metal, the density of the metal, and the time it takes for the push pin to fall from the metal.

metal	density (g/cm^3)	time to fall (sec)
aluminum
copper
iron

Search for densities of copper, aluminum, and iron and add them to your table.
Hold the twisted end with the beaker tongs.
Put on your goggles and light the candle using the matches.
Put the wire apparatus directly into the flame.  Make sure that the flame touches the juncture of all of the wires.
Begin timing how long it takes for each push pin to fall.   If some of the push pins have not fallen after 180 seconds record this as 180+ seconds on your data table.
Produce a line graph in Excel graphing the density of the metal vs the time it took to for the push pin to fall.  Calculate the slope of the line on the graph.
Analyze the graph and report the relationship that exists between density and the time it took for the push pin to fall (conduction of heat).
Add two rows to your spreadsheet, one for silver and one for gold. Look up the densities for silver and gold and add them to your spreadsheet.
Find the slope of the line on the graph using this equation:   
m    =   ( y2  -  y1)/(x2  -  x1) .

Part 2 (Types of Metals)
Add three columns to your data table in excel for V = voltage (volts), I = current (amperes), R = resistance.
Attach one 10 cm piece of copper wire to the negative terminal of the battery and a 5 cm piece of copper wire to the positive terminal.
Hook the free end of the 5 cm copper wire to a light bulb, then run the other 5 cm copper wire from the light bulb to the ammeter.
Feed the 10 cm copper wire free end into the voltmeter.  You should have an open circuit with a space for a wire connection between the ammeter and the voltmeter.  This is where you will insert each 5 cm piece of wire that is to be tested.  See  circuit diagram below:

Insert each piece of wire into the position between the ammeter and voltmeter.
Record the amount of current and voltage that each wire carries.  Calculate the resistance using the equation:

Add these calculations to complete your spreadsheet and create a line graph of the density of the metal and its resistance to the flow of electricity.

Part 3 (Length and Thickness)
Start a new sheet in Excel for keeping track of the data from part 3.  In part 3 you will substitute wires of varying lengths  ( 5 cm, 25 cm, 50 cm)
Using the same apparatus from part 2 insert the copper wires of different lengths.   Place the 5 cm copper wire between the ammeter and voltmeter and record the current and voltage readings on your spreadsheet.
Calculate the resistance R=V/I
Place the 25 cm copper wire between the ammeter and voltmeter and record the current and voltage readings on your spreadsheet
Calculate the resistance.
Place the 50 cm copper wire between the ammeter and voltmeter and record the current and voltage on your spreadsheet
Calculate the resistance
Graph the relationship between the length of the wire and resistance
Make a similar new spreadsheet for different thickness or gauge of copper wire. Now use the copper wires that are of the same length but different gauges (thickness).
Create a graph of how the thickness of the wire affects resistance.

1. Which metal had the highest density?
2. Which metal recorded the quickest conduction time?
3. Explain why metals with higher densities make better conductors of heat.
4. Were these metals also good conductors of electricity?  Why do you think this?
5. If a metal is a good conductor does it have a high or low resistance to the flow of electricity?
6. Which metal that was tested had the least resistance?  Most resistance?
7. By looking at the slope of the line would gold and silver have shorter or longer times for push pin dropping ? Explain your answer.
8. Would you expect gold and silver to have a high or low resistance to the flow of electricity? Why?
9. Using what you learned about conductivity and density which metal (aluminum, iron, copper, silver, or gold) would be the best metal to wire your home? What would be the drawback to using this metal?
10. What does the length of the wire do to the resistance?
11. What is the relationship between thickness of a wire and its resistance?
12. Name at least two variables that must be considered when choosing what type of wire to run from your generator to the houses and businesses on EdVenture Island.