A thin ring of 10 cm radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of 40 π rad s–1 about its axis, perpendicular to its plane. If the magnetic field at its centre is 3.8 × 10–9 T, then the charge carried by the ring is close to (μ0 = 4 π × 10–7 N/A2
(1) 7 × 10–6 C
(2) 4 × 10–5 C
(3) 2 × 10–6 C
(4) 3 × 10–5 C
