A $100\%$ efficient step-down transformer has an input voltage of $240\,\text{V}$ a.c. and an output voltage of $60\,\text{V}$ a.c. If the current in the primary coil is $0.50\,\text{A}$, what is the current in the secondary coil?
- A$0.13\,\text{A}$
- B$0.50\,\text{A}$
- C$2.0\,\text{A}$
- D$8.0\,\text{A}$