to manipulate – How to keep the figure in Graphics at a fixed size

I have the following code:

F[u_] = Graphics[{Circle[{0, 1}, 1]Circle[{2 Sqrt[u], u}, u]}]Manipulate[Show[f[u]], {{u, 0.5}, 1,10}]

Now, if we try the slider, we can actually see that when we make the second circle (the one for which its center and radius depend on $ u $), the first "fixed" circle (the unit circle centered in $ (0.1) $) will decrease the size of the image.

What should I do to make the size of this circle "fixed", that is to say that, whatever the size of the second circle, the first circle remains of fixed size when you use the cursor? (so that the image does not zoom in / out to see both circles)