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.

Activity 7.1: Testing Temperature with Touch

  • Objective: To understand why touch isn’t reliable for measuring temperature.
  • Materials Needed: Three containers labeled A (warm water), B (tap water), and C (ice-cold water).
  • Steps:
  1. Place your right hand in Container A and your left hand in Container C for 1–2 minutes.
  2. Then place both hands in Container B.
  3. Observation: One hand will feel B as cool, while the other feels it as warm.
  • Conclusion: Touch alone cannot be used to measure 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.

Important Questions

  • Q. Can you use a clinical thermometer to measure boiling water?
    • No, this temperature is too high for a clinical thermometer..
  • Q. How do we measure very high temperatures?
    • We use other special types of thermometers designed for those ranges.

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.

Activity: Measuring Temperature with a Laboratory Thermometer

  • Objective: To measure water temperature with a laboratory thermometer.
  • Steps:
  1. Take warm water in a beaker.
  2. Dip the thermometer in the water without touching the sides or bottom.
  3. Observe the rise of the liquid in the thermometer.
  4. Note the temperature when the liquid level stabilizes.
  5. Compare your reading with your classmates.

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.

Scientist Anna Mani

  • Known as the “Weather Woman of India.”
  • Developed various weather measurement instruments and promoted renewable energy in India.

Chapter Summary:

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