Construction of six SEPnet
generator demonstrations

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Dr Jonathan Hare, The Creative Science Centre, May 2012



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In the spring of 2012 I was asked by SEPnet to design, construct and test six generator demonstrations. These will be used to demonstrate Faraday induction (electricity generation). Each kit contains a large search coil with amplifier attached (small black box), a large demonstration meter and two 'paddles'. The two paddles have 4 and 10 magnets attached to them and are used to apply a changing magnetic field to the search coil. When the paddles are moved into the coil the meter registers the current induced into the coil. The meter will give a greater deflection using the 10 magnet paddle than when using the 4 magnet paddle. The meter will also register more current with faster paddle movement. Some of the basic ideas of Faraday induction can be shown with this equipment. The search coil can also register the current induced into the coil by the Earths magnetic field when the coils are picked up and rotated.

For more information about the science and theory please see the following link: SEPnet coil demonstrates electricity generation.
SEPNet coil demonstrates electricity generation - C. Harvey and J. P. Hare, Journal of Physics Education, 2009, 44, p. 603-606.

SEPnet web site.


cutting perspex

Perspex sheet being cut using the router and attached circle cutter



cutting a circle

Close up of circle cutter, cutting a large circle for the search coil.



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Cutting out the paddles (devices used to hold the magnets).



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Jonathan Hare using the router. A router is a noisy and very messy device producing lots of dust. A face mask and ear defenders are essential. Eye goggles are a good idea also.



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The 18 'circles' cut-out (still with protective covers) used to make up the 6 formers for the large search coils.



circuit diagram
Electronic circuit of Jonathan's SEPnet search coil amplifier. In the original device made a few years ago (SEPnet coil demonstrates electricity generation) I used a very sensitive 50uA full scale deflection (FSD) meter. Unfortunately I could not obtain 6 of these so I had to use commercially available demonstration meters. These are not nearly as sensitive requiring about 2.5mA FSD (ca. 50 times less sensitive). As a result I had to build a simple amplifier circuit to boost the voltage from the coil in order to drive the meter. Rcal is used to set the meter to roughly zero for no change in field strength (i.e. no paddle movement near the coil). 100k was found to be about right. The battery test circuit button when pressed, unbalances the amplifier so that the meter reads about full scale for a new / healthy battery.

Coil Specifications
Coil diameter: 38cm on perspex former
Number of turns: 80 turns formed from a 100m reel of bell wire (Maplins: PA56L)
inductance: 5.6mH (measured at 1kHz), coil resistance: 6 ohm


Thanks to Clare Harvey and Charlotte Thorley from SEPnet.

For more information about the science and theory please see the following link: SEPnet coil demonstrates electricity generation.
SEPNet coil demonstrates electricity generation - C. Harvey and J. P. Hare, Journal of Physics Education, 2009, 44, p. 603-606.

SEPnet web site.


THE CREATIVE SCIENCE CENTRE

Dr Jonathan Hare University of Sussex, Brighton.
e-mail: j.p.hare@sussex.ac.uk

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