# الرقم الحثي

{{#category_index:I|induction number}}
A dimensionless parameter used to characterize electromagnetic induction response such that μωσ*L*^{2}=constant, where σ is the conductivity contrast, μ the magnetic permeability, ω the angular frequency, and *L* is a characteristic linear dimension. A full-scale electromagnetic system and a scale-model analog have the same responses if they have the same induction number. For a 1D (layered) model, the induction number is given by the source-receiver separation *R* divided by the skin depth: *B*=*R*/δ=(μωσ)^{1/2}*R*; an equivalent quantity in the time domain is β=(μσ/2*t*)^{1/2}*R*. For an airborne EM system flown at height *h* over a thin sheet of conductivity-thickness product σ*d*, the induction number is (μωσ*dh*)^{1/2}. Frequently several dimensionless parameters of this type are equally valid. Also called **response parameter**.