the potential at the center of curvature of the arc = v = Q ∕ (4πε∘a) or 
ATQ,
We have density of charge,
λ = 
Where L is the rod's length, in this case the semicircle's length L = πr
Q is the charge on the rod
The potential created at the center by an differential element of charge is:

where k is the coulomb's constant
r is the distance from dQ to center of the circle
v = ∫
, Where a = radius, k = 1 / 4πε∘
v =
or Q ∕ (4πε∘a)
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