1) when the resistance R=20 and the current I= 1 1A, U = 1 1 * 20 = 220 V.

The functional relationship between current and resistance is I=U/R, that is, I = 220/r.

2)

When the current borne by the stage route does not exceed 10A.

I = 10

Therefore, I = (220/r) = < 10.

，r > = 22