Evans balance
An Evans balance, also known as a Johnson Matthey magnetic susceptibility balance, is a scientific instrument used to measure the magnetic susceptibility of solids and liquids. Magnetic susceptibility quantifies the extent to which a material becomes magnetized in an applied magnetic field. It can be measured using various devices that modify the shape of the magnetic field and measure resulting forces. The Evans balance operates by measuring the force exerted on a magnet within a magnetic field shared with a sample as an indirect proxy for the magnetization of a sample, rather than by measuring the force exerted on the sample directly.
Source: Wikipedia
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