Magnetic Susebility

Objective
To determine the magnetic susceptibility of a given paramagnetic solution
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Holmarc's Magnetic Susceptibility - Quincke's Method Apparatus (Model No: HO-ED-EM-07) is designed for the determination of magnetic susceptibility of a given solution. The apparatus consists of a pair of electromagnets and a Quincke's tube in which the sample is taken. This tube is U shaped and has two limbs, one with very narrow width compared to the other. So, the change in the level of the liquid in the narrow limb does not affect the level in the wider limb. The magnetic field is measured using a digital Gauss meter. In Holmarc's apparatus, the rise in liquid by the application of magnetic field is measured using a traveling microscope.

On applying magnetic field, the liquid in the Quincke's tube either rise or fall. If the liquid is paramagnetic with respect to the surrounding air , the liquid level will rise and if it is diamagnetic, then the liquid level will fall. In this apparatus, paramagnetic liquid is used and the liquid level will rise.

The Quincke's Method is used to determine magnetic susceptibility of paramagnetic substance in the form of a liquid or an aqueous solution. This method is based on the force experienced by a magnetized material in a non-uniform magnetic field. When an object is placed in a magnetic field, a magnetic moment is induced in it. The magnetic susceptibility is a proportionality constant which is dimensionless and indicates the degree of magnetization of a material in response to an applied magnetic field. A liquid sample in a narrow tube placed between the poles of a magnet experiences a force and hence when the field is turned on, the meniscus in the narrow tube rises by an amount h, relative to its zero-field position. Measuring this rise enables to determine the susceptibility of the solution.

Experiment Examples

    Calibration of the magnetic field

Introduce the gauss meter probe between the poles of electromagnet. Change the current from zero up to its maximum value and from maximum to zero. Note the corresponding field strength from gauss meter at different intervals. Plot a graph Magnetic field Vs Current.

    Measurement of magnetic susceptibility of paramagnetic Solutions

Mass susceptibility of the solution, χ'solution can be obtained from this relation.

χ'solution   =   (  ms / ms + mw  )  χ'salt  +  (  mw / ms+ mw  )  χ'water

where χ'water   =   -0.72 x 10-6, ms is the mass of the salt dissolved in ms of water.