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## Homework Statement

Calculate the magnetic field at point O for the current-carrying wire segment shown in Figure. The wire consists of two straight portions and a circular arc of radius R, which subtends an angle Ɵ. The arrowheads on the wire indicate the direction of the current(Biot–Savart Law).

**2. The attempt at a solution**

##dB = \frac {μ I}{4π} \frac {ds}{R^2}## - I

##B = \frac {μ I}{4π R^2} \int ds = \frac {μ I}{4π R^2} s = \frac {μ I}{4π R} Θ##

Since s=RΘ

I'm little bit confused in the calcualtion of ds in equation I.

##|\vec {ds} \times \hat r| = |\vec {ds}|.1.sin 90^o = ds##

Does ds here represent the magnitude of the vector perpendicular to the vector ##\vec {ds}## and ##\hat r## or it represents the magnitude of orginal vector ##\vec {ds}##.