Question
Twelve equal charges, q, are situated at the corners of a regular 12-sided polygon(for instance, one on each numeral of a clock face). What is the net force on a test charge Q at the center?
Ans
Ans
As shown in the figure charge Q experiences equal and opposite repulsive forces for every pair of q charges situated at the opposite corners of the given 12-sided polygon. Coulomb force exerted by any q charge upon the test charge Q gets nullified by the other q charge sitting at the exact opposite corner. As a result of that Q experiences ZERO net force as whole.