🔍 Key Concepts

• RL circuit behavior when a DC voltage is first applied • Mathematical form of current growth: exponential rise toward a maximum value • Definition of time constant (τ) in terms of percentage of final value

💭 Think About

• When a DC source is suddenly connected to an RL circuit, does the current instantly jump to its maximum or change gradually? How does this relate to τ? • For an exponential rise toward a final value, what fraction (in percent) of the final value is typically reached after one time constant? • Which quantity in an RL circuit (current or voltage across the inductor) is commonly associated with that standard percentage at one time constant?

✅ Before You Answer

• Recall that τ (time constant) describes how fast a quantity approaches its final value in an exponential process. • Know the standard exponential percentages: about 63.2% and 36.8% are complementary (they add to 100%). Which one is the usual definition for τ in a rising function? • Identify whether the current or the voltage across the inductor is the one that follows the standard time-constant percentage for a build-up process in an RL circuit.