Electronic – Is negative resistance possible


I was reading Hayt Kemmerly Engineering Circuit Analysis Book,(I tried others, but this is the most comprehensible to me.), And I came across this circuit. I understand the first two, but I don't understand how, in the 3rd circuit (c), there is negative voltage through the resistor \$R_3\$ , while the current through it from \$+\$ to \$-\$ is positive \$7A\$. I don't understand how resistors can supply voltage. My guess is this is only a mathematical model, not real.

Edit: The Answers are shuffled in this book.
Edit 2: It looks like this book is not in the public domain, as I originally thought. However, I am not removing this image because it falls under fair use.
Hayt Kemmerly Engineering Circuit Analysis

Best Answer

In a passive device, negative absolute resistance cannot exist. However, negative differential resistance, where an increase in voltage leads to a decrease in current or vice versa, is observed in a number of rather common systems, such as neon signage and fluorescent lighting, as well as some more esoteric ones like tunnel diodes. Below is a figure showing an I-V curve for a generic electrical discharge; notice the region between points D and G where the voltage decreases as the current increases. This is the region in which both fluorescent lighting and neon signage normally operate.

A current-voltage curve for a generic electrical discharge. (image source)

Negative absolute resistance can exist over limited ranges by using active elements. There's an op amp circuit commonly called a negative impedance converter that simulates a negative resistance, capacitance, or inductance by using an op amp and feedback:


simulate this circuit – Schematic created using CircuitLab

The two circuits above are equivalent, provided the op amp does not saturate.