A current loop, having two circular arcs joined by two radial lines is shown in the figure. It carries a current of 10 A. The magnetic field at point O will be close to:

Magnetic field due to radial straight segments PQ and RS: $$B_{\text{radial}} = 0$$

Magnetic field formula for a circular arc: $$B = \frac{\mu_0 I}{4\pi R} \theta$$

By Right-Hand Rule, inner arc field ($$B_1$$) is into the page ($$\otimes$$) and outer arc field ($$B_2$$) is out of the page ($$\odot$$):

$$B_{\text{net}} = B_1 - B_2 = \frac{\mu_0 I}{4\pi} \theta \left(\frac{1}{R_1} - \frac{1}{R_2}\right)$$

$$B_{\text{net}} = 10^{-7} \times 10 \times \frac{\pi}{4} \left(\frac{1}{0.03} - \frac{1}{0.05}\right) = 10^{-6} \times \frac{\pi}{4} \left(\frac{100}{3} - \frac{100}{5}\right)$$

$$B_{\text{net}} = 10^{-6} \times \frac{\pi}{4} \times \frac{40}{3} = \frac{10\pi}{3} \times 10^{-6} \approx 1 \times 10^{-5}\text{ T}$$