In the transmission experiment, what can we use to measure the amount of monochromatic light transmitted through a box of rhodopsin?

• A. Radiometer
• B. Spectrometer
• C. Photomultiplier
• D. Light meter

Answer: (A)

Measuring how much monochromatic light passes through rhodopsin is a radiometric task—you want a direct measure of radiant power. A radiometer is designed to detect and read out the amount of radiant energy passing through or hitting a sensor, giving a straightforward, quantitative value for the transmitted light. This is ideal for a transmission experiment because it reports the actual power carried by the light, independent of eye response or wavelength filtering.

In contrast, a spectrometer would tell you how the light is distributed across wavelengths, which isn’t necessary when you’re dealing with a single, monochromatic beam. A photomultiplier detects light with extreme sensitivity by producing an electrical signal proportional to photon flux, but it requires more setup and calibration for absolute power measurements. A light meter measures illuminance with respect to human vision, not the physical radiant power, so it isn’t suitable for precise transmission measurements in this context.