q. Two point charges of +16 micro coulomb and -9 micro coulomb are placed 8 cm apart in air .Determine the position of the point at which the resultant field is zero .
Consider an axial point x cm away from -9 micro C.Then Electric field intensity at that point will be
(k X (16 micro) / (8+x)2 )+(k X (-9 micro) / (x)2 )
But given it is zero so
we have 16/(8+x)2 = 9 / x2
or x / x+ 8 = 3 / 4
or x =24 cm
so Electric field is zero at 24 cm on the axial line from -9 micro C charge