The length of the sparks generated is wholly dependent upon the speed at which the user turns the handle but sparks of around 20-30mm are comfortably achievable.
A hand driven Van de Graaff generator, which is a very effective unit for introducing electrostatics.
Dimensions (H x Dome Dia.): 400 x 200mm.

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Ltekonline are the manufacturers of Van De Graaff Generator Hand Driven Electrostatic Lab used to demonstrate engineering principles in Engineering Colleges, Engineering Schools and Physics Lab Experiments for Engineering Teaching Lab in Universities