In the given circuit the cells have zero internal resistance. The currents (in amperes) passing through resistance $$R_1$$ and $$R_2$$ respectively, are:

$$\text{Potential at top node above } R_1 = 10\text{ V}$$

$$\text{Potential at bottom node below } R_1 = 0\text{ V}$$

$$\text{Potential at top node above } R_2 = 10\text{ V}$$

$$\text{Potential at bottom node below } R_2 = 10\text{ V}$$

Potential difference across $$R_1$$: $$V_1 = 10 - 0 = 10\text{ V}$$

Current through $$R_1$$: $$I_1 = \frac{V_1}{R_1} = \frac{10}{20} = 0.5\text{ A}$$

Potential difference across $$R_2$$: $$V_2 = 10 - 10 = 0\text{ V}$$

Current through $$R_2$$: $$I_2 = \frac{V_2}{R_2} = \frac{0}{20} = 0\text{ A}$$