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TonyDuell · 4th Feb 2019, 6:38 pm

As I understand it, an electrophorus is essentially a variable capacitor (!). You start by charging the capacitor (rubbing the insulator to charge it electrostatically then putting the metal plate above/on it and earthing it to charge that 'by induction'). Now you separate the plates. The capacitance goes down, the charge is constant (the charge can't go anywhere) so the voltage goes up. The energy stored also goes up, but you are not getting something for nothing as you have to do work against the electric field to separate the plates.

And yes, the Wimshurst machine uses a similar principle, the foil pieces on the disks are the capacitor plates.

Getting back to the subject, there was a series of books called 'Fun with ....'.

'Fun with Electricity' certainly described the electrophorus, along with a number of battery/bulb/motor experiments.

There was also 'Fun with Electronics' (or was it 'Fun with Radio'??) which contained some simple valve radio projects and 'Fun with HiFi' which included some valve amplifiers to build (I think the Mullard 3-3 is in there).

4th Feb 2019, 6:38 pm	#40
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,225	Re: Old books/magazines and the gems within As I understand it, an electrophorus is essentially a variable capacitor (!). You start by charging the capacitor (rubbing the insulator to charge it electrostatically then putting the metal plate above/on it and earthing it to charge that 'by induction'). Now you separate the plates. The capacitance goes down, the charge is constant (the charge can't go anywhere) so the voltage goes up. The energy stored also goes up, but you are not getting something for nothing as you have to do work against the electric field to separate the plates. And yes, the Wimshurst machine uses a similar principle, the foil pieces on the disks are the capacitor plates. Getting back to the subject, there was a series of books called 'Fun with ....'. 'Fun with Electricity' certainly described the electrophorus, along with a number of battery/bulb/motor experiments. There was also 'Fun with Electronics' (or was it 'Fun with Radio'??) which contained some simple valve radio projects and 'Fun with HiFi' which included some valve amplifiers to build (I think the Mullard 3-3 is in there).