Two identical cells, when connected either in parallel or in series, give the same current in an external resistance 5 Ω. The internal resistance of each cell i s ______ Ω.

Question

G1 Physics · Accepted Answer

Series current = 2E/(5+2r). Parallel current = E/(5+r/2). Equating them gives 2/(5+2r)=1/(5+r/2), so r=5 Ω.