Friday, July 4, 2014

Leiden Jar Physics Video: Lightning in a Bottle

The capacitor's history begins with the Leiden jar. Benjamin Franklin observed that electricity acts like a fluid, and so, in order to capture the electric fluid, an experiment was conducted at the University of Leiden

In the original experiment, a glass jar, held in the hand, had its inner lining coated with metal and this was charged electrically. Upon touching the inside with the other hand, the experimenter was surprised to receive a horrible shock! The electricity was saved in the jar like a liquid. This is the original "lightning in a bottle" experiment. You've heard of this phrase, right?

These days, the experimenter's hand has been replaced with an outside metal coating on the Leiden jar. The discharging hand has been replaced with a discharging wand. 

Image of a modern Leiden jar being discharged safely 

Most Leiden jars found in the high school classroom are of the plastic, dissectable variety, but many teachers do not know how to use them to their full potential or even safely.

                     A disassembled Leiden jar can be reassembled without loss of charge

In this video, I demonstrate how to safely dissect the Leiden jar and reassemble it, while maintaining the charge. This is one of the most surprising demonstrations in electrostatics.   

Infrared Physics Experiments and Labs

Infrared light was discovered by the simple means of a prism by William Herschel in 1800. The different colors warmed by different amounts, with red being the second-warmest. Red was second only to invisible infrared light, which Herschel discovered by moving the thermometer to a place below the red, where he did not think there would be any light. But there was--infrared light.

A temperature sensitive liquid crystal sheet provides a modern alternative to the thermometer and prism approach (also shown on left)

Many people confused this result with the association of infrared light with heat. Infrared light is actually a focusing effect from the prism. There is a higher energy density because the colors on the red side are squished together. We now know that blue light is more energetic per photon. 

In this video, I wanted to address the history, while also providing fun and practical experiments and demonstrations for the high school classroom.


The most freely available source of infrared light is the TV remote control. Somewhat less common is the thermographic camera, but I was lucky enough to obtain one from Fluke. 

Why should we learn about infrared light? People often have trouble recognizing that their senses are limited, that the human body and human consciousness are not enough to study the natural world fully. 

Infrared light is a good example of a phenomenon beyond human sensation. It is a captivating phenomenon that is within our reach to study in our science classrooms. 

Students will be interested to learn about the infrared sensory organs of snakes. 

Drawing an ice beard