def fn_zeta_over_V(l,N_series,P_nuc):
    """Ratio of electroaxionic tensor component zeta_11 and axion-induced voltage as a function of:
    -- crystal thickness l
    -- the number of crystals used in series N_series
    -- the spin polarization fraction P_nuc.
    """
    return N_series**-1 * P_nuc**-1 * l**-1