SP212
Lesson 28
Ch 30.6 RL Circuits
Problem 1
A solenoid with an inductance of 8.0 mH is connected in series to a 2.0 Ω resistor.
a) What is the the inductive time constant τL for this system?
b) If this system is connected to a 20 V battery, how long will it take for the current through the resistor
to reach 50% of its maximum value? 75%? 87.5%?
c) What is the current through the resistor at time t = τL ?
Problem 2
Suppose the emf of the battery in the circuit shown in the figure varies with time t so that the current is
given by i(t) = 2.00 + 4.00t, where i is in amperes and t is in seconds. Take R = 3.00 Ω and L = 5.00 H,
and find the emf required of the battery at t = 5.00 s.
HINT: Find the current at t = 5.00 s and use the change in potential across the resistor and the inductor
in the loop rule.