Temperature and Its Measurement

Definition of Temperature

Temperature is a reliable quantitative measure of the degree of hotness or coldness of a body or object.

Definition of Thermometer

A device or instrument used to measure the temperature of an object or body is called a Thermometer.

Standard Unit of Temperature

• The commonly used unit in daily life is degree Celsius (°C).

• Another scale mentioned in weather/body fever checks is degree Fahrenheit (°F).

• The SI (Standard International) unit used in science is Kelvin (K).

Purpose and Range

• Used specifically to measure human body temperature.

• Measuring Range: 35°C to 42°C (or 95°F to 108°F).

• Normal healthy human body temperature is approximately 37.0°C (or 98.6°F).

Key Parts & The Function of "Kink"

A classic glass clinical thermometer contains a bulb with mercury (or alcohol) and a long narrow tube. Just near the bulb, there is a tiny bend called a Kink.

• Why is the Kink important? The kink prevents the liquid column from falling back down on its own when the thermometer is taken out of the mouth/armpit. This gives us enough time to take an accurate reading!

Precautions while reading a Clinical Thermometer

1. Wash with an antiseptic solution before and after use.

2. Give a few gentle jerks to bring the liquid level below 35°C before taking temperature.

3. Read keeping the level of liquid along the line of sight (avoid parallax errors).

4. Handle with care! Do not hold by the bulb while reading.

Why switch from Mercury Glass Thermometers to Digital?

• Mercury is a toxic, poisonous chemical element. If a glass thermometer breaks, disposing of mercury safely is extremely difficult.

• Digital Thermometers: Do not use mercury! They run on small battery cells and display readings clearly on a digital screen.

Infrared / Non-Contact Thermometers

These measure thermal radiation from a distance without touching the body. They became popular worldwide during COVID-19 for rapid thermal screening in schools, airports, and hospitals.

Purpose and Measuring Range

• Used to measure temperature during scientific experiments in laboratories (like boiling water, hot oil, chemicals).

• Typical Range: -10°C to 110°C.

Calculating Value of Small Divisions

To read a thermometer accurately, find the value of one small division:

1. Difference between two bigger marks (e.g., between 20°C and 21°C = 1°C).

2. Count total small divisions between them (e.g., 10 divisions).

3. Value of $1\text{ small division} = \frac{1^\circ\text{C}}{10} = 0.1^\circ\text{C}$.

Air Temperature & Weather Reports

• Maximum and Minimum temperatures recorded every day are measured using a special thermometer called Maximum-Minimum Thermometer.

• Air temperature changes throughout the day — lowest in the early morning and highest around noon/afternoon.