Bolometer – working principle and purpose In basic instrumentation terms, a bolometer is best described as which of the following?

Introduction / Context:
Bolometers are widely used in infrared (IR) thermography, astrophysics, and thermal imaging. They translate incident electromagnetic radiation, typically in the IR, into a measurable change in temperature and therefore resistance. Understanding what a bolometer actually measures and how it signals is essential to distinguish it from photonic detectors or general thermometers.

Given Data / Assumptions:

• Incident radiation is absorbed by a sensing element.
• Absorption raises the element's temperature slightly.
• Electrical resistance of the element changes with temperature and is read out.

Concept / Approach:
A bolometer measures radiant power by calorimetric means: optical energy → heat in the absorber → temperature rise → resistance change. The output is electrical (change in resistance or related bridge voltage), not a “thermal output” delivered to the process. This sets bolometers apart from photodiodes/phototransistors (which generate photocurrent via photon–electron interactions) and from gas thermometers or mechanical gauges (which work on expansion or elastic deformation, not radiation absorption).

Step-by-Step Solution:

Verification / Alternative check:
IR camera datasheets describe microbolometer arrays where each pixel is a tiny bolometer, read out electrically to form images of thermal radiation.

Why Other Options Are Wrong:

• Optical input with thermal output: Misleading; the useful output is electrical.
• Photodiode-like visible detector: Different detection physics.
• Gas expansion thermometer: Unrelated to bolometric detection.

Common Pitfalls:
Thinking a bolometer “measures temperature” directly; it measures absorbed radiant power that causes a temperature change in the detector.

Final Answer:
A sensor used for measuring thermal radiation power via temperature-dependent resistance.