Devices with negative-resistance characteristics Which of the following devices exhibit a negative-resistance region in their I–V characteristics?

Introduction / Context:
Negative-resistance devices are essential in relaxation oscillators and trigger circuits. A region of negative differential resistance means that as the voltage increases, current decreases (or vice versa), enabling oscillation and switching behaviors without complex active devices.

Given Data / Assumptions:

• UJT: Unijunction transistor.
• PUT: Programmable unijunction transistor.
• SBS: Silicon bilateral switch.

Concept / Approach:
The UJT and PUT are classic devices used to create sawtooth waveforms and provide triggers due to their negative-resistance region after reaching the peak (for UJT) or firing point (for PUT). The SBS is a symmetrical, two-terminal device that similarly shows a breakover and negative-resistance characteristic used in triggering TRIACs and timing circuits.

Step-by-Step Solution:
UJT: exhibits peak and valley points with a negative slope between them → negative resistance present.PUT: programmable analog of UJT, also shows negative resistance after triggering.SBS: bilateral triggering device with a characteristic similar to a DIAC; negative-resistance region present.Hence all three listed devices exhibit negative resistance.

Verification / Alternative check:
Characteristic curves in component datasheets depict the peak/valley behavior leading to negative differential resistance regions.

Why Other Options Are Wrong:

• Listing fewer devices ignores known behavior of the omitted component(s).
• “None” contradicts standard device physics.

Common Pitfalls:

• Confusing negative differential resistance with simple threshold switching; the former is a slope property of the I–V curve.

Final Answer:
UJT, PUT and SBS