Question

The hand refractometers are calibrated at a temperature of

• A. 15°C
• B. 20°C
• C. 25°C
• D. 30°C

Hint:

Standard optical refractometers are reference-calibrated at $20^\circ\text{C}$ ($n_D^{20}$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Refractometry measures the critical angle of total internal reflection to determine refractive index and dissolved sucrose content ($^\circ\text{Brix}$).

Step 2: Detailed Explanation:
Because the refractive index of liquids decreases with increasing temperature due to thermal expansion, standard optical hand refractometers are calibrated at an international reference temperature of $20^\circ\text{C}$ ($68^\circ\text{F}$) using pure distilled water ($0.0^\circ\text{Brix}$).
Measurements taken at other temperatures require temperature correction factors or automatic temperature compensation (ATC).

Step 3: Final Answer:
Thus, hand refractometers are calibrated at 20°C.