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Re: [Phys-l] Fun/cool unit conversion example?

Bernard Cleyet wrote:
I know caps. are measured in cm, (at one time, why.) How does one obtain mag. flux in Hz?

bc wet?

On 2010, Jan 21, , at 09:46, Brian Whatcott wrote:

of a common gas is mimicked in a NMR spectrometer which uses a 500 MHz magnet? :-)

It's a term of the NMR trade. Put less succinctly, Larmor found that there is a relation between the frequency of an emitted signal from a proton rich material and the magnetic field ('strength') in which it is immersed. The relation is of a particularly simple, satisfying kind - which leads to an absolute instrumental measure of the size of the geomagnetic field, for example.
In terms of the nanoTesla (nT) and proton spin relaxation frequency (Hz) as put in classical terms.... B0 (nT) = 23.496241 x F (Hz)

A more familiar example is to find that a bottle of water subject to a uniform magnetic field, emits a small signal when that magnetic forcing field is removed.
For a geomagnetic amplitude of 47 microTesla or 47000 nT, the emitted frequency is 2 kHz.
The signal in several hundred turns of wire amounts only to microvolts, and that fades in very few seconds, but its frequency is an absolute measure.

Or, to get finally to the point: a proton spin relaxation signal can be set at 500 MHz if the test magnetic field strength is set to 11.74... Tesla
In this field a sample of nitrogen 15 will provide a signal at 50.66MHz
This is the frequency at which I expect JohnD's cap and coil to resonate.

See for example a mention in the second page of this paper in J Phys Chem B at

or more properly: FischBach et al, J. Phys. Chem. B 2004, 108, 18500-18508

(It is no great pleasure to offer a trail of crumbs, along which I have to post pointers too.....)