One technique for measuring the coefficient of this effect for a sample is to use an arrangement with four contacts named for van der Pauw. A type of spacecraft thruster named for this effect ionizes a gaseous propellant and then expels it using an electric field. In a semiconductor, the coefficient of this effect must take the hole mobility into account. In the inversion layer of a field effect transistor, the energy levels induced by this effect are quantized, as predicted by (*) von Klitzing. Its coefficient is inversely proportional to the carrier density, and this effect offers proof that carriers are negatively charged. For 10 points, name this effect in which 
One technique for measuring the coefficient of this effect for a sample is to use an arrangement with four contacts named for van der Pauw. A type of spacecraft thruster named for this effect ionizes a gaseous propellant and then expels it using an electric field. In a semiconductor, the coefficient of this effect must take the hole mobility into account. In the inversion layer of a field effect transistor, the energy levels induced by this effect are quantized, as predicted by (*) von Klitzing. Its coefficient is inversely proportional to the carrier density, and this effect offers proof that carriers are negatively charged. For 10 points, name this effect in which a transverse voltage appears in a conductor when a magnetic field is applied.
One technique for measuring the coefficient of this effect for a sample is to use an arrangement with four contacts named for van der Pauw.
Hall effect [accept more specific answers like quantum Hall effect, fractional quantum Hall effect, integer quantum Hall effect, etc.]