Five point charges each of charges +q are placed of five vertices of a regular hexagon of side 'l'. Find the magnitude of the resultant force on a charge -q placed at the centre of the hexagon.
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Explanation

From the adjoining it is that force on -q charge placed at centre point O due to A and B are respectively balanced by force due to D and E respectively.
` therefore ` Magnitude of resultant force =Force due to charge C
` " " =F= (1)/(4 pi in _0) .((q)(q))/(l^(2)) `
`rArr " " F= (1)/(4pi in _0) .(q^(2))/(l^(2))`