### Neet Solved Paper 2015 Question 32

##### Question: An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude

#### Options:

A) $ \frac{{\mu _0}ne}{2\pi r} $

B) zero

C) $ \frac{{\mu _0}n^{2}e}{r} $

D) $ \frac{{\mu _0}ne}{2r} $

## Show Answer

#### Answer:

Correct Answer: D

#### Solution:

As $ I=\frac{q}{t} $ So, for an electron revolving in a circular orbit of radius r q = e and t = T

$ \Rightarrow \ I=\frac{e}{T}=\frac{e}{2\pi /\omega }=\frac{\omega e}{2\pi }=\frac{2\pi ne}{2\pi }=ne $

The magnetic field produced at the centre is $ B=\frac{{\mu _0}I}{2R}=\frac{{\mu _0}ne}{2r} $