A circular coil with 5 turns, each of radius 7 cm, carries a current of 1.4 A. The magnetic field at the center of the coil is

$2π×10^{-5} T$

The correct answer is Option (4) → $2π×10^{-5} T$

Given:
Number of turns, $N = 5$
Radius, $r = 7\,cm = 0.07\,m$
Current, $I = 1.4\,A$

Magnetic field at the center of a circular coil:

$B = \frac{\mu_0 N I}{2r}$

Substitute values:

$B = \frac{4\pi \times 10^{-7} \times 5 \times 1.4}{2 \times 0.07}$

$B = \frac{4\pi \times 10^{-7} \times 7}{0.14}$

$B = 4\pi \times 10^{-7} \times 50$

$B = 2\pi \times 10^{-5}$