A circuit contains four identical resistors connected as illustrated. The battery has negligible internal resistance and an e.m.f. of $30\,\text{V}$. What is the potential difference between points X and Y?
- A$6.0\,\text{V}$
- B$15\,\text{V}$
- C$20\,\text{V}$
- D$24\,\text{V}$