Answer
$f=1.8\times 10^7 Hz$
Work Step by Step
The centripetal force is produced by Magnetic force.
So,
$F_c=F_m$
$\frac{mv^2}{R}=qvB$
or $R=\frac{mv}{qB}$..................eq(1)
We know that the angular frequency is given as
${\omega}=\frac{v}{R}$
Substituting the value of 'R' from eq(1), we obtain:
$\omega=\frac{v}{\frac{mv}{qB}}$
or $\omega=\frac{qB}{m}$.......................eq(2)
But we also know that $\omega=2\pi f$
or $f=\frac{\omega}{2\pi}$
Substituting the value of $\omega$ from eq(2), we obtain:
$f=\frac{\frac{qB}{m}}{2\pi}$
or $f=\frac{qB}{2\pi m}$
We now plug in the known values to obtain:
$f=\frac{1.602\times 10^{-19}(1.2)}{2(3.1416)(1.67\times 10^{-27}}$
$f=1.8\times 10^7 Hz$
