A thin ring of 10 cm radius carries a uniformly distributed charge. The ring rotates at a constant angular speed of `40pi "rad s"^(-1)` about its axis, perpendicular to its plane. If the magnetic field at its centre is `3.8xx10^(-9)T`, then the charge carried by the ring is close to `(mu_(0)=4pi xx10^(-7)N//A^(2))`

Options

A. `7 xx 10^(-6)` C
B. `4 xx 10^(-6)` C
C. `2 xx 10^(-6)` C
D. `3 xx 10^(-5)` C

Answer

D

Explanation

`B = (mu_(0))/(4pi) (qv)/(r^2) ""sin theta implies B = 10^(-7) (q omega r)/(r^2)`
`q = (3.8 xx 10^(-4))/(4pi ) implies q = 3 xx 10^(-5) C`