Thunderbolts and lightning, but not so frightening!
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Thunderbolts and lightning, but not so frightening!

Last week’s thunderstorms were a great segue to a DP Physics lesson about electricity. After showing the students an abysmally bad quality video that I took the night before as I tried to capture some lightning bolts on film, the class wondered – how does lightning come about?

by Mikko Peltonen, secondary physics and maths teacher

It is not an easy one to answer, especially as scientists don’t exactly know all the little details of the process. When teaching the topic, demonstrations and experiments are still possible, and useful. A Van de Graaff generator is a stable piece of equipment at science classrooms.

Van de Graaff generator; www.britannica.com

In this particular lesson, it was used to create artificial lightning bolts (students also had some fun throwing Styrofoam pieces on it and seeing them bounce back with a surprisingly great force, generated by the electric field around the metal dome). The picture shows a spark between the two metal spheres.

Floating lettuce seeds

Demonstrations like these are essential to help learners see microscopic or otherwise invisible phenomena of nature. Last week the students explored the different shapes electric fields can take by way of lettuce seeds floating in a petri dish where two electrodes with high voltage were inserted. The seeds arranged themselves along the electric field between the electrodes, as you can see in the picture above.

Ice crystals

So, how is lightning formed? The basic principle is that within a thundercloud, tiny ice crystals are pushed upward by air pressure, while heavier hails are pulled down. The icy particles collide with each other and the smaller ones give off electrons to the heavier hail, making the top part of the thundercloud positively charged and the bottom part negatively charged. Now, sparks can occur within the cloud, or between the cloud and the ground, as negative electrons move to make everything electrically neutral again.

Spark

Hopefully the students will maintain the spark generated by the demonstration and stay engaged until the upcoming final exam week!