Question

Charge q is uniformly distributed along a thin semicircular arc of radius r

Answer 1

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Answer 2

The semi circular charge with radius R is shown in blue. The incremental arc element ds has a charge, dq = rho R ds where rho is the linear charge density for the differential arc length. By symmetry we can see that Ex = integral(dEx) from 0 to Pi is going to equal zero. But not Ey.