Q.Van de Graaff generator is an electrostatic machine which produces (A) Only high current
(B) Only high voltage
(C) High current and high voltage
(D) Low current and low voltage

A Van de Graaff generator produces very high voltages (of the order of millions of volts) but only small currents.

In a Van de Graaff generator, charge is carried by a moving belt to a large hollow metal sphere, where it accumulates on the outer surface. Because the sphere is a conductor, added charge spreads over its surface and its potential keeps rising, reaching very high values (up …

The charge accumulated on the Van de Graaff sphere works out to about 0.66 millicoulomb.

A charged conducting sphere of radius $R$ carrying charge $Q$ has a surface potential $V = \dfrac{1}{4\pi\varepsilon_0}\dfrac{Q}{R} = \dfrac{kQ}{R}$, where $k = 9\times10^9\ N\,m^2\,C^{-2}$.

Given: diameter $=2\,m \Rightarrow R = 1\,m$; $V = 6\times10^6\,V$.

$Q = \dfrac{VR}{k} = \dfrac{(6\times10^6)(1)}{9\times10^9} = 6.67\times10^{-4}\,C = 0.667\ \text{milli coulomb} \approx 0.66\ \text{milli coulomb}$

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