Photometer is used to measure

Analysis of the Question

The question asks for the specific function of a photometer in the context of physics. To answer this, we need to distinguish between instruments used for measuring light properties (intensity, wavelength, frequency) and those used for particle physics (like the photoelectric effect).

Concept Explanation

• Photometer: The word is derived from "photo" (light) and "meter" (measure). It is a scientific instrument used to measure the intensity of electromagnetic radiation, specifically visible light. It works by converting light energy into an electrical signal, which can then be measured.
• Kinetic energy of electrons: This is typically measured using a retarding potential apparatus in experiments related to the photoelectric effect (often associated with Millikan’s experiment).
• Frequency/Wavelength of light: These are usually measured using a spectrometer or an interferometer, which separates light into its component colors or measures the interference patterns of light waves.

Step-by-Step Solution

1. Define the instrument: A photometer is designed to quantify the strength or "brightness" of a light source at a specific point or over a surface.
2. Evaluate the options: • A: Incorrect. Kinetic energy of electrons is related to the photoelectric effect, not photometry. • B: Correct. Photometry is defined as the science of the measurement of light in terms of its perceived brightness to the human eye, which is essentially the intensity of light. • C: Incorrect. Frequency is a property of the wave itself, usually measured via spectroscopy. • D: Incorrect. Wavelength is also a property of the wave, measured via diffraction or interference methods.

Conclusion

Based on the standard definition of optical instruments in Physics, a photometer is specifically used to measure the intensity of light.

Exam Tip: When you see "meter" at the end of a physics term, think about what is being measured.

• Photo-meter: Light intensity.
• Spectro-meter: Spectrum (wavelength/frequency).
• Galvano-meter: Small electric currents.
• Calori-meter: Heat energy.