In order to measure the properties of a battery, several resistors are connected to the battery in series and the terminal voltage is measured. In the first case, the resistor has resistance R1 = 3.5 Ω and the terminal voltage is ΔV1 = 2.9 V. In the second case, the resistor has resistance R2 = 77 Ω and the terminal voltage ΔV2 = 7.5 V.
Required:
Find the numerical value of r in Ω.