Chapter 7 — Temperature and its Measurement

Chapter 7 of Class 6 Science (Curiosity) is about temperature — what it is, how we measure it, and the different scales (Celsius, Fahrenheit, Kelvin) used to express it. It also covers clinical and laboratory thermometers and their correct use.

Our sense of touch gives relative feelings, not absolute temperature values. For example, after one hand is in warm water and the other in ice-cold water, both placed in tap water will feel different temperatures — the hand from warm water feels it as cool, while the hand from cold water feels the same tap water as warm.

The normal temperature of a healthy human adult is taken to be 37.0 °C (98.6 °F). A perfectly healthy person may have a temperature slightly different from this, as it is an average of many healthy people. It does not normally go below 35 °C or above 42 °C.

The three scales are: (1) Celsius scale — unit is degree Celsius (°C); (2) Fahrenheit scale — unit is degree Fahrenheit (°F); (3) Kelvin scale — unit is kelvin (K, no degree sign). Kelvin is the SI unit of temperature.

Temperature in Kelvin = Temperature in Celsius + 273.15. For example, 37.0 °C = 37.0 + 273.15 = 310.15 K. Absolute zero is 0 K = –273.15 °C.

A clinical thermometer is used to measure human body temperature and is designed for the narrow body-temperature range. A laboratory thermometer is used for many other purposes and has a wider range of –10 °C to 110 °C. A clinical thermometer cannot measure temperatures like boiling water or ice.

The typical range of a laboratory thermometer is –10 °C to 110 °C. The smallest value it can read depends on the number of divisions. For the thermometer in the textbook with 10 divisions between each 10 °C mark, the smallest readable value is 1 °C.

An infrared thermometer can measure a person's temperature without touching the body. Such non-contact thermometers were widely used during the COVID-19 pandemic to reduce the risk of spreading disease between people.

Absolute zero is the lowest temperature that can theoretically be achieved. It is 0 kelvin, which equals –273.15 °C. There is no limit on the highest temperature that can exist; for reference, the core of the Sun reaches 15 million degrees Celsius.

Mercury is an extremely toxic substance. If a mercury thermometer breaks accidentally, the mercury is difficult to dispose of safely. Digital thermometers pose no such risk and their readings are easier to see on the display.

Anna Mani (1918–2001) was an Indian scientist known as the 'Weather Woman of India'. She invented and built a large number of weather measurement instruments, reducing India's reliance on other nations. She also explored wind and solar energy possibilities in India, helping India become one of the global leaders in renewable energy.

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