In the Classroom

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This activity should only be conducted by an individual who is experienced working with electricity. Science Discipline(s) Physical Science Topics
  • Physical properties
  • Light transmission
  • Energy Transitions
Activity Title Pencil Lead Light Bulb Materials
  • Mechanical Pencil Lead (0.5mm and 0.7mm graphite)
  • 8 D cell batteries
  • Electrical Tape
  • Insulated metal wire (battery to pencil lead, length as needed)
  • Alligator Clamps (4x)
  • Alligator clamp stand (optional)
  • Heat/Electrical insulating gloves
  • 1 Clear Glass Jar
Procedure
  1. Attach 1 alligator clamp to each end of a length of wire. (Repeat 2x)
  2. Attach the 0.5 mm pencil lead to the alligator clamps in such a manner that it is sturdy, and will not move during the experiment, preferably use a stand, however, they can also be taped to the edge of a table such that the graphite will not burn anything when it gets hot.
  3. Don safety gloves, and attach ONE of the 2 wires to the battery/electrical source.
  4. After making sure that the graphite is in a safe position, and the audience is aware that it will soon get very hot, and be an exposed bare wire, attach the other wire to the battery/electrical source.
  5. The pencil lead should light up. Depending on the diameter of the lead, it may take a short amount of time so begin glowing, wait 5-10 seconds before resetting the experiment.
  6. When finished, DISCONNECT THE BATTERY, and then with thermally protective gloves, remove the pencil lead. It is hot and should be treated as such.
    Questions
  1. Why did the lead glow?
  2. How could you test the effect of voltage and current (e.g., the number of batteries) on how brightly the lead glowed?
  3. What kinds of energy transfer is taking place (there’s more than 1)?
  4. Why was the thicker lead dimmer?
Explanation While graphite can conduct electricity, it is a poor conductor. As the electricity flows from one battery terminal to the other, it meets a lot of resistance within the graphite filament. That resistance causes the wire to heat up. The thinner the diameter, the more resistance, and the faster it will heat and the brighter it will light up. More batteries would also increase the brightness as more electricity would flow through the lead. Once the graphite heats up enough, it will start to glow as the electrons are excited to higher energy states. Next Generation Science Standards This experiment would be best conducted in a 4th grade setting as students are just beginning to learn about not only energy transfer but also electrical flow. This experiment not only helps to demonstrate how electrical energy can be transferred to heat, and heat energy can then be transferred to light, but also how different diameter measurements of the same materials have different resistances. 1-PS4-2.          Make observations to construct an evidence-based account that objects in darkness can be seen only when illuminated. [Clarification Statement: Examples of observations could include those made in a completely dark room, a pinhole box, and a video of a cave explorer with a flashlight. Illumination could be from an external light source or by an object giving off its own light.]PS4.B: Electromagnetic Radiation 4-PS3-2.          Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents. [Assessment Boundary: Assessment does not include quantitative measurements of energy.] 4-PS3-4.          Apply scientific ideas to design, test, and refine a device that converts energy from one form to another.* [Clarification Statement: Examples of devices could include electric circuits that convert electrical energy into motion energy of a vehicle, light, or sound; and, a passive solar heater that converts light into heat. Examples of constraints could include the materials, cost, or time to design the device.] [Assessment Boundary: Devices should be limited to those that convert motion energy to electric energy or use stored energy to cause motion or produce light or sound.]   5-PS1-3. Make observations and measurements to identify materials based on their properties. [Clarification Statement: Examples of materials to be identified could include baking soda and other powders, metals, minerals, and liquids. Examples of properties could include color, hardness, reflectivity, electrical conductivity, thermal conductivity, response to magnetic forces, and solubility; density is not intended as an identifiable property.] [Assessment Boundary: Assessment does not include density or distinguishing mass and weight.]   MS-PS4-2.      Develop and use a model to describe that waves are reflected, absorbed, or transmitted through various materials. [Clarification Statement: Emphasis is on both light and mechanical waves. Examples of models could include drawings, simulations, and written descriptions.] [Assessment Boundary: Assessment is limited to qualitative applications pertaining to light and mechanical waves.]   References https://www.youtube.com/watch?v=wLBZdYDks10 http://yale.edu/demos/files/Week3PencilLeadLightBulb.pdf