1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution My answer to (b) was that power supply would have an internal resistance which is not negligible and will affect results. The correct answer is that shorted lamp A would cause damage to the lamps/supply. How is lamp A shorted? I don't see how there is a short cut way for the current to flow through to short lamp A. And how can we measure the resistance of the lamps by using an ohm meter without any power supply?