LIGHTNING CRASHES

Build a Franklin bells device for detecting high voltage lightning storms

RN: 11030202 - ELECTRICITY & MAGNETISM > STATIC ELECTRICITY

SUITABLE GRADES

7 & 8

DIFFICULTY

3

TIME REQUIRED

<1 week

SUPERVISION

REQUIRED

INTRODUCTION [METHOD]

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:

STUFF YOU NEED [MATERIALS]

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

HOW TO PROCEED [PROCEDURE]

Electricity & magnetism science project - Static electricity

Clean two empty soda cans and remove the pull tops from each of the cans.
Tie a piece of sewing thread about 150mm in length to one of the pull top lids.
Tie the other end of the thread to a pencil or plastic pen so that the pull top lid hangs about 100m below the pencil when it is held horizontally.
Stand the two soda cans side-by-side on top of an old CRT television or computer monitor so that they are spaced about 50mm apart.
Place the pencil horizontally on top of the two cans, so the pull-tab is suspended freely about 30mm from the surface.
Use two insulated wires of about 600mm – 1000mm in length with alligator clips to both ends. Tape the bare end of one of the wires to the left can to form the 'ground' wire. Connect the free end of the 'ground' wire to an electrical ground, such as a cold water pipe. If an electrical 'ground' is not available, you can just hold onto the free end, as your body would be a good enough 'ground' for this device.
Use sticky tape to tape the remaining wire to the soda can on the right. This wire's free end will be connected to a source of high voltage.
Press a 300x500mm piece of aluminium foil onto the face of the TV screen, and hold it in position with sticky tape. When the TV screen is switched on, it becomes highly charged with electricity and the foil will stick to the screen. Connect the free end of the wire in step '7' to the piece of aluminium foil.
Start the device by turning on the TV. The pull-top lid gets pulled to one can, but when it hits it, it gets pulled to the other can, and then repeats!

WHY IT WORKS [CONCLUSION]

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GLOSSARY [TERMS]

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