Science Fair this week

We took a weekend off the previous week as Daphne and I went on our first vacation away from the kids to Asheville NC.  This weekend was the finial prep week for Noelle's (age 9) science fair.  The plan had been to do a light bulb with veggies but we couldn't track down a LED with low enough power requirements (the best we got was 2.5 V and 20mA  which Noelle calculated as needing a grid of 3 potatoes in series for the voltage by 60 in parallel for current @ 0.9V and 0.33 mA per spud in her logs).  I'm just going to post her report from her own words and some of the photos she took.

What Pencil Lead Makes the Best Light Bulb?

Materials:

• Filament (pencil leads 0.5, 0.7, and 0.9 mm)
• Power source (8 C cell batteries - 12 volts total)
• Glass bulb (jar)
• Connecting wires
• Alligator clips (to hold the filament)
• Wooden block (to hold the clips in the jar)

How a light bulb works:

Electricity flows from the power source through the filament in the light bulb to create heat and light. Electrons move through the wires and filament when it's connected to the battery. Some of the moving electrons run in to atoms in the filament causing them to become hot and emit light.

Procedure:

1. Assembled the light bulb with materials including electrical tape to hold things in place.
2. Measured and attached pencil lead (one size and length at a time) to the alligator clips.
3. Place jar over filament to reduce air and burning, as well for protection when it breaks.
4. Attach the power source and start a timer to measure duration.
5. Make observations while it burns about brightness.
6. When it burns out, stop timer and record results.

Results:

Filament size -1/2 inch

0.5mm – 19 seconds, 19 seconds, and 18 seconds

0.7mm – 40 seconds, 41 seconds, and 48 seconds
0.9mm – 100 seconds and 165 seconds (we were concerned about the battery so we only did 2 tests)

Brightness:

The thinner filaments glowed brighter than the thicker ones though for a shorter duration. As the thicker leads burned, they grew thinner and they also became brighter. The thick leads were only bright for the last few moments of their life.

Conclusions:

I think that the 0.5 leads made the best light because they were consistently brighter. They also don't burn out the batteries getting hot enough to be bright. With more time we could try changing the length of the filament as well as try other materials. Sealing the jar with play dough or putty might also affect the light and duration. Being careful of the clips and filament after they burn is important because they get VERY hot!

By Noelle Stam

4^th grade Ms. LeClair

April 13, 2011

Measuring the filament length before each burn

burned out 0.5 mm filament

0.7 mm starting to glow somewhat slower than the 0.5 mm

0.9 mm not glowing at all in the beginning though some some is made

0.9 mm barely glowing initially

0.9 mm glowing brighter

0.9 mm filament finally starts to glow bright as it thins.

Partially burned 0.9mm filament shows thinning.