#### 3.1 Polymer Chain in Tension

For example, in elongation of a polymer chain due to tension, we may assume these blobs are more or less lined-up
along the direction of deformation. The number of blobs is (N∕g) so that the extension R ≈ ξ (N∕g). From this, we
see that

The free energy of the chain is increased in tension due to the restriction of the degrees of freedom of the blobs -
each blob in this case contributes kT and so

If we consider the force required to stretch the polymer coil

| (9) |

we see that the blob defines a length scale over which the elastic energy is ≈ kT. That is, under an external force,
the polymer will be unperturbed on length scales smaller that that for which the corresponding ‘thermal forces’ are
kT or larger.