Why does RL natural response have a negative voltage?
This RL Natural Response Polarity Reference video looks at the potentially confusing difference between reference polarity voltage and the physical voltage values during resistor-inductor natural response, including how polarities appear in the use of Kirchhoff’s law.

For technical background on resistor-inductor natural response, see this book:
“First and Second Order Circuits and Equations – Technical Background and Insights”. Published by John Wiley & Sons, Inc., the book “First and Second Order Circuits and Equations”, (called “1st & 2nd” for short) is available here:
[ Ссылка ]
Section 5.3, “First-Order Natural and Step Response Overview” introduces RL natural response, (side-by-side with RC natural response for greater insight), on page 63. Section 7.1 shows RL natural response in terms of discharging, generated by switch circuits, from pages 149-152. RL natural response is formally derived from time domain differential equations on pages 161-163, including the evaluation of the constants of integration using initial conditions. A second and alternative differential equation solution approach is shown on page 165.

There is also a video on “RC Circuit Natural Response Reference Polarity”
[ Ссылка ]

For a video on RC natural response derivation, please see my video:
RC Circuit Natural Response Derivation v(t)
[ Ссылка ]


00:00 Introduction
00:27 RL Natural Response Current
01:06 Natural Response Equation
01:22 Negative Inductor Current Graph
02:14 Resistor Reference Polarity
02:34 Resistor IV Characteristic
03:00 Inductor Branch Relationship
04:01 LTspice RL Natural Response Simulation
04:45 Reference Polarity and KVL
05:01 Reference Polarity Opposite Currents
05:22 KVL Counterclockwise
05:49 Resistor Reference Polarity
07:03 Branch Relationships into KVL
07:44 Change Inductor Reference Polarity
08:19 KVL Current Polarity Both References
09:49 Final Polarity Test Question

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