Manoj Sahu said:
Thank you very much. But is it possible to demonstrate it using some equipment. I am doing a small scale project so buying or employing Van De Graff generator is not feasible.
A Van De Graaff generator is a rather simple device and you'll find hundreds of DIY online plans, some better than others. But I don't know how effective, or efficient building one would be for your project. You say you are building a lightning detector. What is your mode of detection? If you're measuring an E-M spike then any device which can produce such would be sufficient. An ignition coil and a 12v battery could be sufficient if close enough to your device.
There's an inverse square law for propagation of waves (of any type) in space which means that moving your source 10 times closer makes it 100 times more powerful in effect so it need only be 1/100th as powerful to start with. According to the font of all knowledge and truth, Wikipedia, a typical lightning bolt is a 5billion joule event.
Assume you want to detect say a somewhat weaker bolt (1 billion joules) that is as far as 10 km away.
Well then a discharge 10cm = 1/10th meter away, 1/100,000 as far need only be 1/10,000,000,000 as powerful which is a 10th of a joule. So you need a discharge within about that order of magnitude within 10 cm. Note that at 5cm it need only be 1/4th as much but our calculation is getting a bit sketchy at this point as we're in the near field range at typical SW VHF and the inverse square business breaks down there.
(Since c = 30million meters per sec, a 30megahertz wave has 1m wavelength and 300megahertz wave has wavelength 1/10 m = 10cm.)
So something in the 10 to 100 milli-joule range discharge at a 3 to 10cm distance should do. An automotive
ignition coil produces on the order of 50millijoules (again according to wikipedia) per spark so at the worst hold your project next to (~3cm from) the ignition wires of a running automobile but better might be to find a used ignition coil and some online instructions to make a specific spark generator.
Have fun and do be careful not to electrocute yourself.
I'm serious about that last part. Here's a link about safety with Van de Graaff generators which includes some general info about electrical safety: http://practicalphysics.org/van-de-graaff-generator-safety.html