A straightforward circuit consists of a source of electromotive force (e.m.f.) linked to a load. In what way does the source’s output power $P$ vary with the source’s internal resistance $r$ and the load resistance $R$?
- A$P$ is independent of both $r$ and $R$.
- B$P$ depends on $r$ but not on $R$.
- C$P$ depends on $R$ but not on $r$.
- D$P$ depends on both $r$ and $R$.