In an RC circuit, the time constant is defined as:

Core Concept

The time constant (τ) of an RC circuit is defined as the product of resistance and capacitance, τ = RC. It represents the time it takes for the capacitor to charge to approximately 63.2% of its maximum charge or to discharge to approximately 36.8% of its initial charge. Options A, B, and D describe aspects of RC circuit behavior but are not the definition of the time constant itself.