In a double-beam spectrophotometer, how many detectors are used and how many beam splitters are there?

• A. 2 detectors, 1 beam splitter
• B. 1 detector, 1 beam splitter
• C. 2 detectors, 2 beam splitters
• D. 3 detectors, 1 beam splitter

Answer: (A)

In a double-beam spectrophotometer, light is split into two simultaneous paths so that sample and reference can be measured at the same time. A single optical element called a beam splitter divides the incoming light into two beams, one going through the sample and the other through the reference. Each beam then reaches its own detector, so two detectors are needed to capture the intensities of both beams independently. This arrangement helps cancel out fluctuations in the light source and drift in the detectors, improving accuracy.

Using more than one beam splitter isn’t necessary and would reduce light intensity and complicate alignment, while a single detector couldn’t monitor both beams at once without time-sharing, which defeats the purpose of simultaneous comparison.