Question

A colorimeter (photometric) determination involves the measurement of colour in which region of the electromagnetic spectrum?

• A. Infrared
• B. Ultraviolet
• C. Visible
• D. Microwave

Hint:

Colorimetry = visible light absorption. Spectrophotometry = visible + UV + IR regions.

Answer 1

The Correct Option is C

Step 1: Recall principle of colorimetry.
A colorimeter measures the absorbance of light by a coloured solution. The amount of light absorbed is proportional to the concentration of the solution, according to Beer-Lambert’s law.
Step 2: Which region is used?
Color is a property of visible light, which lies between wavelengths of 400–700 nm. Hence, a colorimeter works in the visible spectrum.
Step 3: Exclude incorrect options.
- (A) Infrared: Used in IR spectroscopy, not in colorimetry.
- (B) Ultraviolet: Used in UV spectrophotometry.
- (C) Visible: Correct, since colorimetry measures absorption in the visible region.
- (D) Microwave: Used in communication and radar, not in photometry.
Step 4: Conclusion.
Colorimetric determination involves measurement in the visible region of the electromagnetic spectrum.