Magnetic susceptibility of a material is defined as the ratio of the intensity of magnetisation (I) induced in the material to the magnetisation force (H) applied on it. Magnetic susceptibility is represented as: Substances such as copper, lead, etc. have negative susceptibility. These substances are called diamagnetic substances. Substances such as aluminium, calcium, etc. have positive susceptibility. These substances are called paramagnetic substances. Substances with negative susceptibility signify that they are repelled by magnets.