Temperature and Its Measurement

Introduction to Temperature: Hot or Cold

Understanding Hot and Cold:

• We can feel if something is hot or cold by touching it, but this (Sense of touch) isn’t always accurate.
• Example: Tap water in summer may feel hot compared to water from an earthen pot.
• Key Point: Our sense of touch can be misleading in judging temperature accurately.

Temperature

• Temperature is a measure of how hot or cold something is.
• A hotter body has a higher temperature than a colder one.
• We measure temperature with a thermometer.

Types of Thermometers:

1. Clinical Thermometer: Measures body temperature.
2. Laboratory Thermometer: Used for scientific purposes.

1. Clinical Thermometer:

• Purpose: Measures body temperature.
• Normal Range: Around 37°C (98.6°F).
• Instructions for using a Clinical Thermometer:
  • Wash the thermometer tip with soap and water.
  • Reset the thermometer.
  • Place it under the tongue until it beeps.
  • Read the temperature on the display.

2. Laboratory Thermometer:

• Purpose: Used in scientific experiments to measure temperatures of substances.
• Structure:
  • Glass tube with a bulb containing mercury or alcohol.
  • A Celsius scale (usually from -10°C to 110°C) marked on the tube.
• Important: Not for measuring body temperature.

3. Infrared Thermometer:

• Measures temperature from a distance without direct contact.
• Commonly used for quick temperature checks, especially was used during COVID-19.

Temperature Scales

• 1. Celsius (°C):

• Commonly used scale.
• Normal human body temperature: 37°C.

• 2. Fahrenheit (°F):

• Commonly used in the United States.
• Normal body temperature: 98.6°F.

• 3. Kelvin (K):

• Used in scientific experiments.
• Formula to convert Celsius to Kelvin: K = °C + 273.15.

Laboratory Thermometer:

Definition:

• A laboratory thermometer is a device used to measure temperature in laboratories.

Structure:

1. Made of a long, thin glass tube.
2. A bulb at one end containing a liquid (usually alcohol or mercury).
3. A Celsius scale marked on the tube.
   • The liquid expands and rises when heated, showing the temperature on a Celsius scale.
   • The liquid rises or falls depending on temperature changes.

Range:

The range means the lowest and highest temperatures the thermometer can measure.

• Typically range, -10°C to 110°C.

How to find the smallest value a thermometer can measure?

• Check the temperature difference between two big marks (e.g., between 0°C and 10°C).
• Count the small divisions between them.
• Example: 10 divisions between 0°C and 10°C means each small division equals 1°C.

Precautions:

• Handle it carefully (glass can break if hit).
• Do not hold it by the bulb (this may affect the reading).
• Always read the thermometer while it’s in the substance being measured.

Correct way to use a laboratory thermometer:

• Do not let the bulb touch the sides or bottom of the beaker.
• Hold the thermometer vertically.
• Read the temperature while the thermometer is still in the water.
• Your eye should be at the same level as the liquid in the thermometer.

Air Temperature

• Thermometers placed on walls measure room temperature.
  • example – walls of a school or clinic can have such Thermometers.
• Daily weather reports include maximum and minimum air temperatures.

Chapter Summary: