A wire with length $L$ has resistance $R$. Its cross-section is a circle of radius $r$. Another wire, which also has a circular cross-section and is made from the same material, has resistance $\frac{1}{2}R$. What pair of radius and length might the second wire have?
- Aradius $\frac{r}{2}$, length $\frac{L}{2}$
- Bradius $\frac{r}{\sqrt{2}}$, length $\frac{L}{2}$
- Cradius $r\sqrt{2}$, length $2L$
- Dradius $2r$, length $2L$