Question

You short-circuit a 9 volt battery by connecting a short wire from one end of the battery to the other end. if the current in the short circuit is measured to be 18 amperes, what is the internal resistance of the battery?

Answer 1

R = V / I .

R = (9 v) / (18 A) = 0.5 ohm . (Measure fast. The battery is dead in about 1/2 a second when you do this.)

Answer 2

The internal resistance of the battery will be = 9/18 = 0.5 Ω