This is the problem I'm working on:
A loop of wire has the shape of two concentric semicircles connected by two radial segments (See figure). The loop carries a current $I = 280.00 A$. Find the magnetic field at point $P$. ($R = 21.00 cm$)
So I the magnetic field due to an arc to be $B = (\mu_0I/2\pi)(\alpha/r)$, which, if we take $r = 2R$ for the top arc and $r = R$ for the bottom arc, and $\alpha = \pi/2$ for both arcs, we get:
$B=(\mu_0I/4)(1/2R - 1/R)$
The answer I'm getting using this equation is wrong. Where is my mistake? Am I going down the correct path for this question?