A variable resistor is made from a metre of resistance wire. The resistance of the whole length of wire is 80 ohms. If you had a 6 V battery and wanted to provide 3.7V to power your iPod directly, how would you connect up this variable resistor and battery?

A variable resistor R is connected across the terminals of a battery. FIGURE shows the current in the circuit as R is varied. What are the emf and internal resistance of the battery?

Two resistors of X and Y are connected in parallel with oneanother and in series with a 200 Ω resistor and a battery e=1.5V and internal resistance r=0.5 Ω. The resistance ofX is 100 Ω. When Y is disconnected from X, an additional resistanceof 50 Ohms must be inserted in the circuit in order to keep thecurrent through X unchanged. Find the resistance of Y. Compute thevalue of Y again for the same case considering the internalresistance of the battery negligible.