The diagram illustrates a circuit designed to regulate the potential difference (p.d.) across a lamp. The variable resistor is altered until the p.d. across the lamp reaches $6.0\,\text{V}$. The current through the lamp is $0.5\,\text{A}$. What is the resistance of the lamp?
- A$0.083\,\Omega$
- B$3.0\,\Omega$
- C$6.5\,\Omega$
- D$12.0\,\Omega$