As the strength of the magnetic field increases, what happens to the rate of precession?

• A. the rate of precession increases
• B. the rate of precession decreases
• C. the rate remains the same
• D. the rate fluctuates

Answer: (A)

The rate of precession is set by the Larmor frequency, which is proportional to the magnetic field strength. In a magnetic field, a magnetic moment experiences torque that makes it precess about the field direction at angular frequency ω = γB, where γ is the gyromagnetic ratio. So increasing B gives a faster precession because the torque grows and the moment sweeps around the field axis more quickly. This relationship is linear in the ideal case.

So when the magnetic field gets stronger, the precession rate increases; it does not stay the same or fluctuate in a steady field, and it does not decrease with a stronger field.