Apparatus Competition

2007 AAPT Summer Meeting

Greensburo, NC

 

Demonstrating Electrical Resistance Factors of Metal Conductors

 

William E. Semrau

VanBuren Intermediate School District

250 South St.

Lawrence, MI  49064

 

269-674-8001

techscienceguy@yahoo.com

 

 

Assembly Directions:

  1. Gather materials from local building supply / home improvement store.
  2. Screw metal boxes onto board.
  3. Cut 1 meter (approx) off the female end of the extension cord, leaving the male end to plug into the wall when you are finished. You will need this section later.
  4. Strip back 30 cm of the outer insulation off the cut end of the cord
  5. Knock out 2 holes on both metal boxes & install romex clamps into these 4 holes.
  6. Feed hot/black wire from cord through one romex clamp and attach to one of the brass screws on the fuse/switch.
  7. Cut off 20 cm (approx) from the female end of the extension cord.  Strip back the outer insulation.  Strip back 1.5 cm (approx) of insulation from each end of the black wire (according to strip gauge on back of duplex).
  8. Attach one end to one of the screws on the fuse/switch.  Then put the other end through the 2nd romex clamp and attach one of the alligator clips.
  9. Screw fuse/switch down into box and tighten romex clamps.
  10. Feed white and bare wires from the extension cord through one romex clamp on the 2nd box.  Strip back wire insulation and attach to neutral (white) and ground (bare) screws.
  11. Cut another 20 cm (approx) from the female end of the extension cord and attach to hot screw on the outlet.  Push though 2nd romex clamp and attach alligator clip.
  12. Attach duplex outlet to box and install outlet cover plate.
  13. Wrap alligator clips where hot wire attaches with electrical tape as well as the wires between the fuse and outlet for safety.
  14. Install fuse.  Apparatus is now ready to use.

 

Parts List

 

 

 

 

 

 

Materials

Supplier

SKU #

Quantity

Cost

 

Assembly of Demonstration Apparatus

 

 

 

 

 

30cm x 50 cm board (approx) "Bargin Boards"

Menards

1029666

1

1.69

 

Metal gang box

Menards

361-1218

2

1.58

.79 each

Duplex outlet

Menards

363-3348

1

0.39

 

Duplex outlet cover plate

Menards

361-1221

1

0.59

 

T-type fuse & switch

Menards

367-6868

1

5.96

 

15 Amp T-type fuse, reset

Menards

367-7249

1

6.47

 

14 gauge indoor/outddor extention cord

Menards

370-0433

1

3.48

 

Alligator clip (2/package)

Menards

364-1987

2

0.89

 

Romex cable clamps (4/package)

Menards

365-1003

4

1.19

 

Multi-purpose screws #8 x 3/4" (25/package)

Menards

234-6270

4

1.97

 

Electrical tape (3rolls/package)

Menards

364-6004

1

1.29

 

Equipment:

 

 

 

 

 

Digital Multi Meter with clamp

Harbor Freight Tools

42396

1

15.99

 

Wire: Consumables

 

 

 

 

 

18 gauge Aluminum 50'

Menards

235-1720

1

1.99

 

19 gauge Stainless Steel 30'

Menards

235-1725

1

3.36

 

16 gauge Brass 25'

Menards

235-1715

1

5.49

 

24 gauge Copper 100'

Menards

235-1711

1

6.99

 

28 gauge Brass 75'

Menards

235-1716

1

2.49

 

22 gauge galvanized Steel  100'

Menards

235-1948

1

1.19

 

MIG Welding filler wire 10'

VBISD Welding Program, or any MIG weld shop

1

0.50

 

 

 

 

 

 

 

 

 

 

Total Cost:

63.50

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

24 gauge Copper Speaker wire (stranded) 100'

Menards

301-4941

1

4.98

 

 


Demonstrating Electrical Resistance Factors of Metal Conductors

Directions for Usage:

 

  1. Leave devise in “OFF” position anytime you are changing or installing a wire between the alligator clips.
  2. Cut a section of the “female” end of the extension cord.  It needs to be long enough to reach between the 2 alligator clips.  Strip back insulation and attach to clips.
  3. Plug apparatus into standard 120Vac outlet, turn switch to “ON” position.
  4. Set clamp meter to 20 Amps AC.  Clamp around hot wire between fuse and outlet. (Use a student volunteer to be in charge of  observing and announcing the amperage readings)
  5. Plug in any tool: drill, grinder, toaster, hair dryer, etc and turn on. ( 2nd student volunteer)
  6. Record Amperage.
  7. Plug in a second tool and record amperage. (3rd student volunteer)
  8. Run both tools and record amperage.
  9. Students will see that amperage goes up as more tools are running (a reinforcement of earlier concepts; adding loads in parallel increases amperage).
  10. Use DMM’s thermocouple and set to Celsius or Fahrenheit.
  11. With tools off (amperage = 0), hold the thermocouple a few cm from the end so body heat is not being read as well as a safety factor to keep fingers from current carrying wires.  Place on exposed edge of wire and record temperature. (4th  student volunteer)
  12. Turn 1st tool back on and record temperature of wire. Repeat for 2nd tool only, as well as both tools together.
  13. Students should see that temperature goes up with increased amperage.
  14.  SHUT SWITCH OFF
  15. Replace wire with one of the smaller copper wires purchased separately.
  16. Turn switch on, run tool, and record amperage and temperature data.
  17. Amperage will be the same as before, yet a noticeable temperature increase will occur with each successively thinner copper wire.
  18. Ask students to explain why the temperature increased.  Most of my students, by now, can explain resistance in terms of friction, and with the smaller wire, to move the same number of electrons (same amperage) they will be more collisions in the smaller wire and therefore a higher temperature. Explain in terms of electrical resistance.
  19. Replace copper wires with other wires (aluminum, steel, etc.)  Repeat experiment.  Record temperate data. 
  20. Have students make note of what they observe as they compare data.
  21. Summarize class demo/lab:
    1. Thinner wires get hotter to carry the same amperage
    2. Different wires have different temperatures even with the same amperage
    3. The more amperage a wire carries, the hotter it gets.
    4. Don’t use extension cords that are thinner than the tool you are plugging in
    5. Safety, safety, safety! 
  22. Extension: have students calculate the resistance of the wire