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LIGHTNING CRASHES

Build a Franklin bells device for detecting high voltage lightning storms

Suitable For

Grade 8

Difficulty

3

Time Required

 <1 Week

Supervision

Required

What’s it about?

In 1752 Benjamin Franklin made a device he called Franklin’s bells for detecting approaching lightning storms. He did this by placing two bells adjacent to each other with a metal ball suspended in between them. One bell was electrically connected to the earth and the other was connected to a lightning rod on his roof.

Electrical charge would then build up on the bell connected to the lightning rod, which would then attract the metal ball. As the metal ball comes in contact with the bell, it would be charged similarly and be repelled again. The opposite charged bell will then attract the ball towards it, but when the ball touches the second bell, the charge is transferred and the process repeats, making a ringing sound and indicating a possible lightning storm.

We will use soda cans instead of bells and a TV screen to produce high voltage to simulate his lightning detector in the following science experiment:

Topics covered

Benjamin Franklin, Static electricity, Grounding

What will I need?

  • PENCIL
  • 2x EMPTY SODA CANS
  • SEWING THREAD
  • STICKY TAPE
  • ALUMINIUM FOIL
  • INSULATED WIRE WITH ALLIGATOR CLIPS

Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

This science experiment represents a safer version of a ‘Franklin Bells’ lightning storm detector by using the CRT screen as a high voltage source instead of a real lightning rod. A direct strike to a lightning rod could be very dangerous and cause explosions and fire. The can on the right is connected to the high voltage from the CRT screen and the can on the left is connected to the ground, which will absorb all of the voltage sent to it. The right can builds up electrical charge from the screen and attract the pull-tab suspended from the thread to it.

As soon as the pull tab comes in contact with the right can, it becomes charged to the same potential and hence will be repelled again. The lightning rod would allow charge to build up on the bell, which would then attract the metallic ball. When the ball hits the first bell it will become charged to the same potential, and therefore will be repelled again. The opposite charged can on the left will then attract the ball towards it, and again, when the pull-tab touches the can, the charge is transferred and the process repeats, making a ringing sound similar to the one used by Franklin to detect lightning!

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