The Magnetic Prandtl number (Prm) is a dimensionless quantity occurring in magnetohydrodynamics which approximates the ratio of momentum diffusivity (viscosity) and magnetic diffusivity. It is defined as:
where: is the magnetic Reynolds number is the Reynolds number is the momentum diffusivity (kinematic viscosity) is the magnetic diffusivity
At the base of the Sun's convection zone the Magnetic Prandtl number is approximately 10−2, and in the interiors of planets and in liquid-metal laboratory dynamos is approximately 10−5.
See also Prandtl number
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