An iron wire is $8.0\,\text{m}$ long and has a diameter of $0.50\,\text{mm}$. Its resistance is $R$. A second iron wire is $2.0\,\text{m}$ long and has a diameter of $1.0\,\text{mm}$. What resistance does the second wire have?
- A$\dfrac{R}{16}$
- B$\dfrac{R}{8}$
- C$\dfrac{R}{2}$
- D$R$