What component selects specific wavelengths in a spectrophotometer?

What component selects specific wavelengths in a spectrophotometer?

• A. Grating monochromator
• B. Photomultiplier
• C. Quartz cuvettes
• D. Deuterium lamp

Answer: (A)

The main idea is that isolating a single wavelength in a spectrophotometer is done by a monochromator. Light from the source is a broad mixture of wavelengths, and the grating monochromator uses a diffraction grating to spread that light into its component wavelengths. By adjusting the grating angle and the entrance/exit slits, it allows only a narrow band of wavelengths to pass through to the sample. This selected wavelength is what the instrument analyzes, so the absorbance corresponds to a defined wavelength. The other parts have different roles: the photomultiplier is the detector that converts transmitted light into an electrical signal, the quartz cuvettes hold the sample, and the deuterium lamp is a UV light source that can provide UV wavelengths but does not by itself select a specific wavelength.

The main idea is that isolating a single wavelength in a spectrophotometer is done by a monochromator. Light from the source is a broad mixture of wavelengths, and the grating monochromator uses a diffraction grating to spread that light into its component wavelengths. By adjusting the grating angle and the entrance/exit slits, it allows only a narrow band of wavelengths to pass through to the sample. This selected wavelength is what the instrument analyzes, so the absorbance corresponds to a defined wavelength. The other parts have different roles: the photomultiplier is the detector that converts transmitted light into an electrical signal, the quartz cuvettes hold the sample, and the deuterium lamp is a UV light source that can provide UV wavelengths but does not by itself select a specific wavelength.