Answer:
The potential for r > rb is equal to zero.
Explanation:
For r > rb, the potential is:
[tex]V=\frac{Kq}{r}[/tex]
Then, the net potential is:
[tex]V_{(r)} =\frac{K(+\epsilon )}{r} +\frac{K(-\epsilon )}{r}[/tex]
[tex]K=\frac{1}{4\pi \epsilon _{o} }[/tex]
[tex]V_{(r)} =\frac{K(+\epsilon )}{r} -\frac{K(\epsilon )}{r}\\V_{(r)}=0[/tex]