The interaction energy of the London force is inversely proportional to the sixth power of the distance between two interacting particles but their magnitude depends upon
London forces are present in polar molecules and monoatomic nonpolar molecules like H2, O2, N2, He, Ne, Ar etc., which shows no bonding and exist with intermolecular forces.
The non-polar molecules are electrically symmetrical, so there is no dipole moment, but sometimes temporary dipoles can be formed. The non-polar molecule develop momentarily dipole due to unsymmetrical electronic charge.
INTERACTION ENERGY 
1/r6
‘r’ is the internuclear distance between two interacting particles.
These type of forces work only at a short distance of approximately 500 pm. The magnitude of forces depends on the polarisability of atom or molecule. Polarisability is the ease with which electron and nuclei get displaced for their positions. Stronger the London force, larger the polarisability.