Van de graaff generator.

Van de graaff generator is used to produce a parallel homogeneous beam of charged particles like electrons, protons,α-particles etc. It was developed by van de graaff in 1931 at Princeton university, USA.

Principle:-

The instrument is based on the following two facts:

(i) If a charged conductor is brought into internal contact with a hollow conductor, all of its charge transfers to the hollow conductor, no matter how high is potential of the latter.

(ii) The discharge of electricity  occurs readily at pointed objects (corona points).