An electric field of 300 V/m is confined to a circular area 10 cm in diameter. If the field is increasing at the rate of 20 V/m-s, the magnitude of magnetic field at a point 15 cm from the centre of the circle will be:

1.85 × 10^–18 T

$B =\frac{\mu_0 \varepsilon_0}{2 \pi R}\left(\frac{\pi d^2}{4}\right) \frac{d E}{d t}$

$=\frac{2 \times 10^{-7} \times 8.85 \times 10^{-12} \times 3.14 \times 0.01 \times .20}{4 \times 0.15}$ = 1.85 × 10^–18 T