A Level Physics Practice Exam

What happens to the internal resistance of a power source as current increases?

1. The internal resistance decreases

2. The internal resistance remains constant

3. The internal resistance increases

4. The internal resistance oscillates

The correct answer is: The internal resistance increases

The internal resistance of a power source generally increases as current increases due to several factors related to the physical properties and dynamics of the components within the power source, such as batteries or generators. As the current flowing through the power source rises, it can lead to an increase in heat generated within the internal components. This heating affects the resistance of the materials; for example, resistance in conductive materials usually increases with temperature due to the increased vibrational energy of the atoms, which impedes the flow of electrons. Moreover, some power sources may also experience changes in their chemical composition or physical structure when subjected to higher currents, further contributing to an increase in internal resistance. In devices like batteries, higher currents can lead to increased polarization and possible depletion of active materials, causing the effective resistance to rise. In contrast, a decrease in internal resistance or oscillatory behavior would not be typically observed in standard power sources under increasing load conditions. Instead, a constant internal resistance does not adequately account for the thermally and chemically influenced changes that occur with current flow.