Voigt–Thomson law describes anisotropic magnetoresistance effect in a thin film strip as a relationship between the electric resistivity and the direction of electric current:^[1]

${\displaystyle \rho (\vartheta )=\rho _{0}+\Delta \rho \cdot cos^{2}\vartheta }$

where:

${\displaystyle \vartheta \ }$ is the angle of direction of current in relation to the direction of magnetic field

${\displaystyle \rho _{0}\ }$ is the initial resistivity

${\displaystyle \Delta \rho \ }$ is the change of resistivity (proportional to MR ratio)

The equation can also be expressed as:^[2]

${\displaystyle \rho (\vartheta )=\rho _{\parallel }\cdot cos^{2}\vartheta +\rho _{\perp }\cdot sin^{2}\vartheta }$

where:

${\displaystyle \rho _{\parallel }\ }$ is the parallel component of resistivity

${\displaystyle \rho _{\perp }\ }$ is the perpendicular component