Which of the following terms is associated with 'time constant' in an electric circuit?

The term 'time constant' in an electric circuit is primarily associated with 'exponential decay.' In RC (resistor-capacitor) and RL (resistor-inductor) circuits, the time constant is a measure of how quickly the circuit responds to changes in voltage or current. Specifically, for an RC circuit, the time constant is defined as the product of resistance (R) and capacitance (C), denoted as τ (tau). This time constant determines the rate at which voltage across the capacitor charges or discharges.

During this charging or discharging process, the voltage or current in the circuit changes in an exponential manner. For example, when a capacitor charges through a resistor, the voltage across the capacitor increases exponentially towards its maximum value, with the time constant indicating how long it takes for the voltage to reach approximately 63.2% of that maximum value. Similarly, the voltage will decay exponentially as the capacitor discharges.

The other terms listed, while important in the study of electrical circuits, do not directly relate to the concept of time constant in the same way. Reactance refers to the opposition to alternating current due to capacitance or inductance, while frequency pertains to how often a cyclic event occurs in a given time period