A battery with emf and internal resistance is connected to an external resistor
PHYSICS · Single correct · A Level · Physics · Electricity · Electricity
Problem
A battery with emf 12V and internal resistance 2Ω is connected to an external resistor 6Ω. A second identical 6Ω resistor can be added either in series with the external resistor (Option A) or in parallel with it (Option B). Which option causes the battery to dissipate more power in its internal resistance, and why?
(a) Option A, because the series resistor increases the voltage drop across the battery's internal resistance, so it dissipates more power.
(b) Option B, because adding a resistor in parallel makes the external resistance larger, forcing more power to be lost inside the battery.
(c) Option B, because the total resistance is smaller, so the current (and therefore I2r power in the internal resistance) is larger.
(d) Option A, because the total resistance is larger, and P=E2/r gives a greater internal power loss.