Why does the molar conductivity decrease with increasing charge density?

This is a question in a problem sheet I have been set. Is it do do with the following equation: $\Lambda=\Lambda\_0-a\sqrt c$? Surely charge density is proportional to concentration so therefore molar conductivity would decrease linearly with the square root of concentration (and $c$ $\alpha$ charge density?). Also, what is the physical origin of this equation; my lecture notes simply say that the ions interact with each other, is it as simple as that?


The second part to this question asks "Does the actual conductivity decrease?". Presumably by "actual conductivity", he means $\kappa$ where $\kappa=\Lambda c$. I have no idea about this part so any help would be much appreciated. 


