Cyclotron resonance

1. Jan 14, 2015

Matt atkinson

1. The problem statement, all variables and given/known data
Calculate the lower limit of the electron scattering time in a material placed in a magnetic field of 1 T which is necessary to observe cyclotron resonance. The electron effective mass in the material
is 0.06 $m_o$ (where $m_o$ is the free electron mass).

2. Relevant equations
$\omega_c=\frac{eB}{0.06m_o}$
$\tau_{min}=\frac{2\pi}{\omega_c}$

3. The attempt at a solution
So I basically substituted values into $\omega_c$ and then into the equation for $\tau_c$ i got $\tau_c=2.14ps$ whereas the answer says $\tau_c=0.54ps$, have I gone wrong? or is the solution given wrong, because i have done it multiple times.

2. Jan 15, 2015

Staff: Mentor

The two answers differ by a factor of 4 (+-2%). I guess they took 1/4 of a cycle to be sufficient (some electrons won't scatter for 4 times the scattering time). There is no absolute limit, a shorter time just makes observations harder.

3. Jan 15, 2015

Matt atkinson

ah okay! Thankyou very much I did notice the factor of 4 difference just wasn't sure where it came from.