An industrial electromagnet can be modeled as an RL circuit, while it is being energized with a voltage source. If the inductance is 10 H and the wire windings contain 3 ?of resistance, how long does it take a constant applied voltage to energize the electromagnet to within 90% of its final value (that is, the current equals 90% of its asymptotic value)?

SolutionStep 1 of 5In this problem we have to determine the time required to energize an electromagnet to 90% of its final value (90% of asymptotic value) by applying a constant voltage source.Step 2 of 5We know that the equation for current in a series RL circuit is given byWhere E - Applied voltage R - Resistance of the circuit - time constant of the circuitStep 3 of 5Given L = 10 H, R = 3 ==When the circuit is operating at 90% of its final value, we can write