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Overview

The Laboratory Thermometer

January 15, 2025
1 min read
laboratory experiments measurement

Structure

A laboratory thermometer consists of a long, narrow, uniform glass tube with a bulb at one end.

  • Liquid: Generally alcohol (colored red) or mercury.
  • Scale: Celsius scale is marked along the tube.

Range

Typically, a laboratory thermometer measures from −10∘C-10^{\circ}\text{C} to 110∘C110^{\circ}\text{C}.

-10010110

Calculating Least Count (Smallest Value)

To read a thermometer accurately, you must know the value of the smallest division.

  1. Find the difference between two bigger marks (e.g., 10−0=10∘C10 - 0 = 10^{\circ}\text{C}).
  2. Count the number of divisions between them (e.g., 10 divisions).
  3. Divide the difference by the number of divisions.
Value of one small division=10∘C10=1∘C\text{Value of one small division} = \frac{10^{\circ}\text{C}}{10} = 1^{\circ}\text{C}

Correct Usage

When measuring the temperature of water or other substances:

  1. Immerse: The bulb should be surrounded by the substance.
  2. Do Not Touch: The bulb should not touch the bottom or sides of the container.
  3. Hold Vertically: Keep the thermometer upright.
  4. Read While Immersed: Do not take the thermometer out of the liquid to read it. The level will fall immediately.
  5. Eye Level: Your eye must be in line with the top level of the liquid column to avoid parallax error.
Warning

Caution: Laboratory thermometers are NOT used for body temperature because the liquid level falls as soon as it is removed from the body. Clinical thermometers have a “kink” or digital memory to hold the reading.