Infrared thermometer works on the principle of which of the following radiation laws?

Correct option is B

The correct answer is (B) Stefan–Boltzmann’s Law

Explanation:
• An Infrared (IR) thermometer measures the surface temperature of an object by detecting the infrared energy it emits.
• It is based on the Stefan–Boltzmann Law, which states that the total energy radiated per unit surface area of a black body is directly proportional to the fourth power of its absolute temperature ($E = \sigma T^4$).
• By measuring the intensity of the infrared radiation (the 'E'), the instrument can calculate the absolute temperature ('T') of the object without making physical contact.
• This is widely used in agriculture to measure crop canopy temperature as an indicator of water stress.

Information Booster:
• Emissivity is a key factor in IR thermometers; it is the measure of how efficiently a surface emits thermal radiation compared to a perfect black body.
• Crop Water Stress Index (CWSI) is often calculated using canopy temperature data from IR thermometers.
• These devices are also known as "laser thermometers" if they use a laser to help aim the sensor.

Additional Knowledge:
• Beer’s Law (Option A): Relates the attenuation of light to the properties of the material through which the light is traveling (used in spectrophotometry).
• Wien’s Law (Option C): States that the wavelength of peak emission is inversely proportional to the absolute temperature (helps determine the "color" of the radiation).
• Kirchhoff’s Law (Option D): States that for an arbitrary body in thermodynamic equilibrium, emissivity is equal to absorptivity.