Two large parallel vertical conducting plates separated by distance d are changed so that their potentials are (+V sub 0) and (-V sub 0).(adsbygoogle = window.adsbygoogle || []).push({});

A small conducting ball of mass m and radius R (where R<<d) is hung midway between the plates.

The thread of length L supporting the ball is a conducting wire connected to ground (at V=0)

The ball hands straight down in stable equilib when V sub 0 is sufficiently small.

Show that the equilib of the ball is unstable if V sub 0 exceeds the critical value k*d^2*mg/(4RL)

(Hint: consider the forces on the ball when it is displaced a distance x<<L.)

Thanks very much for answering! :-)

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# Homework Help: Electric Potential (w/ a pendulum :P)

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