In what situation would you observe thermal runaway happening?

Thermal runaway is a situation that occurs when an increase in temperature causes a component to draw more current, which in turn increases its temperature further. This creates a feedback loop that can lead to catastrophic failure of the component.

In this context, the correct answer highlights that thermal runaway is observed specifically when excess current leads to uncontrollable temperature rises in components. For example, if a semiconductor device like a transistor experiences higher than expected current levels due to overheating, it can become less efficient and start to draw even more current, thus further increasing its temperature. This process continues until the component fails, often resulting in melting or destruction of the component.

The other scenarios suggest conditions where components operate within safe limits, indicating no excessive current or voltage fluctuations. In these situations, the components remain stable and function as expected, which would prevent the occurrence of thermal runaway.