Hi,

i have to calculate the molar magnt. suscep. of copper (the result is given, chi= **-72,3E-12 m**^{3} mol^{-1}), that means i have to find the approach to this solution.

This is the exercise: A diamagnetic copper bar with a cross section of 1 cm^{-2} is at 298K in air in a gouy balance. After switching on the magnetic field, one measures a force of 3,95E^{-4} N, if this magnetic field has a strength of H = 8,00E5 Am^{-1} on one end and H = 8,00E3 Am^{-1} at the other end. What is the molar magnetic susceptibility of copper, if the molar magnetic susceptibility of Nitrogen -151E-12 m^{3} mol^{-1} and of Oxygen 42,9E-9 m^{3} mol^{-1} is. The composition of air is 79 Vol% Nitrogen and 21 Vol% Oxygen. The density of copper is 8,96 g cm^{-3}.

In the attachment you can see my solution, the formula of this gouy balance is well known.

My problem is, i donĀ“t know how to calculate the susceptibility of air (Chi (a)). This term must be negative to get the given result (which is a negative term). Can i neglect the paramagnetiv influence of oxygen?

It would be great, if you could give me some hints, to get the result (which is already given).

thanks, goebki