A charge 'q' coulomb is circulating in an orbit of radius 'r' meters making n revolutions per sec. The magnetic field (in N/Am) produced at the center of circle is
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( \displaystyle\frac{2\pi nq}{r} \) × 10-7
A charge going round a circle is a current loop. The charge q passes any point of the orbit n times per second, so the current is
\( \displaystyle I = qn \)
The field at the centre of a circular loop is
\( \displaystyle B = \frac{\mu_0 I}{2r} = \frac{4\pi\times10^{-7} \times qn}{2r} \)
\( \displaystyle B = \frac{2\pi nq}{r} \times 10^{-7}\,\mathrm{T} \)
The unit N/Am (N A−1 m−1) is the tesla.