As the seventh- and eighth-grade science curriculums have evolved to address more advanced topics, much more sophisticated equipment is in order. The Brighton Education Fund has funded the purchase of several pieces not often found in middle school science labs, including an ascending arc induction coil.
This device is also called a "Jacob's Ladder," in reference to a Biblical character who envisioned a ladder to heaven with angels ascending and descending on it. It consists of two vertical conducting bars close together at the bottom and farther apart at the top, like a pair of television "rabbit ears."
A high voltage electrical discharge is applied by connecting a high voltage power supply to the two bars, between which a discharge strikes at the bottom, rises to the top, then restrikes at the bottom.
The ascending arc illustrates electrical discharges and the variation of the density of air with temperature. It can serve as an introduction to a discussion of the physics of plasmas (ionized gases) and electrical breakdown. If it is operated inside a closed tube, the tube fills with a red-brown oxide of nitrogen. The oxide may then be aspirated through water to form nitric acid, illustrating the fixation of atmospheric nitrogen by lightning. The Ascending Arc can also be used to convert oxygen gas (O2) into ozone (O3), a pungent, highly-reactive allotrope of oxygen.
story by Ed Chi and Lawrence Root
photo by Gretchen Shafer
May 28, 2001