Question

A point charge $Q(=3\times {10}^{-12}C)$ rotates uniformly in a vertical circle of radius R = 1 mm. The axis of the circle is aligned along the magnetic axis of the earth. At what value of the angular speed $\omega$, the effective magnetic field at the center of the circle will be reduced to zero? (Horizontal component of Earth’s magnetic field is 30 micro Tesla)

• A. ${10}^{11}rad/s$
• B. ${10}^{9}rad/s$
• C. ${10}^{13}rad/s$
• D. ${10}^{7}rad/s$

Answer 1

The correct option is A ${10}^{11}rad/s$

$\frac{{\mu }_0}{2R}\left(\frac{\omega .q}{2\pi }\right)=30\times {10}^{-6}So\omega ={10}^{11}rad/s$