1.

Consider an arbitrary electrostatic field configuration. A small test charge is placed at a null point (i.e., where E=0) of the configuration. Show that the equilibrium of the test charge is necessarily unstable.

Answer»

SOLUTION :LET us consider that initially the test charge is in the STABLE EQUILIBRIUM. When the test charge is displaced from the null point (where, E = 0) in any direction, it must experience a restoring force towards the null point.
This MEANS that there is a net inward flux through a closed surface around the null point. According to the Gauss's theorem, the net electric flux through a surface net enclosing any charge must be zero. Hence, the equilibrium is not stable.


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