The current noise indices (C.N.I.) depend linearly on the logarithmic values of sheet resistivity (log ρS), in both carbon black/resin and thallium oxide/glass resistors, and can be expressed as
C.N.I. = A + B log ρS. The geometrical dependency on C.N.I. in both types of resistor can be expressed as
C.N.I. = A′ − B′ log (L, W, T), where A, B, A′ and B′ are constants.
The dependency of noise e.m.f. (νn) on the applied dc voltage (V), i.e., the values of α in νn2¯∝Vα, can be obtained from the slope of C.N.I. versus log (L) lines, associated with a model based on the noise generator approximation.