Chapter 7: Temperature and its Measurement
7.1 Hot or Cold?
- Our sense of touch is subjective and unreliable for accurately judging the hotness or coldness of an object.
7.2 Temperature and Thermometers
- Temperature: A reliable, quantitative measure of the hotness or coldness of a body.
- Thermometer: A device used to measure temperature.
Temperature Scales
- Celsius scale: Denoted by °C. Water freezes at 0 °C and boils at 100 °C under standard conditions.
- Fahrenheit scale: Denoted by °F. Historically used for clinical measurements.
- Kelvin scale: Denoted by K. It is the SI unit of temperature.
- Conversion Formula: Temperature in Kelvin (K) = Temperature in Celsius (°C) + 273.15.
7.3 Measuring Temperature
7.3.1 Clinical Thermometer
- Clinical Thermometer: Specifically designed to measure human body temperature.
- Range: 35 °C to 42 °C (human body temperature does not normally go beyond these limits).
- Normal Body Temperature: 37.0 °C (equivalent to 98.6 °F).
- Digital Thermometers: Modern, safe alternatives that use heat sensors instead of toxic mercury.
- Infrared Thermometers: Non-contact devices that measure temperature from a distance, reducing disease transmission risk.
- Precautions: Wash the tip before/after use, keep the digital display out of water, and do not hold it by the tip.
7.3.2 Laboratory Thermometer
- Laboratory Thermometer: Used for measuring temperatures in scientific experiments.
- Range: Typically -10 °C to 110 °C.
- Liquids Used: Generally red-coloured alcohol or mercury.
- Correct Usage: Must be held vertically, the bulb must not touch the bottom or sides of the container, and it must be read while still immersed in the substance.
7.3.3 Air Temperature
- Measured using room thermometers to monitor indoor or outdoor environmental temperatures.
- Weather stations track daily maximum and minimum air temperatures for forecasting.
- Anna Mani (1918–2001): Known as the "Weather Woman of India", she was an pioneering Indian scientist who designed and built numerous weather-measuring instruments, promoting self-reliance in meteorology and renewable energy.