NCERT Curiosity · Class 6 · Science
Temperature and its Measurement
Lambok feels feverish. His sister touches his forehead — but can touch alone really tell us how hot something is?
Key idea
Touch Alone Can Fool You
Dip your right hand in warm water and your left in ice-cold water. Then put both hands into a third bowl of tap water.
The same tap water feels cool to the hand that was in warm water, but warm to the hand that was in ice-cold water.
We cannot always rely on our sense of touch to correctly judge how hot or cold something really is.
Key idea
Temperature and the Thermometer
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Temperature
A reliable measure of the hotness or coldness of a body. A hotter body has a higher temperature than a colder one.
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Thermometer
A device that measures temperature. Clinical thermometers measure body temperature; laboratory thermometers are used for many other purposes.
Key idea
Clinical Thermometers
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Digital
Uses heat sensors and shows a reading on a screen. Runs on a battery.
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Infrared
Measures body temperature from a distance without touching — used widely during COVID-19.
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Mercury (old style)
Being phased out — mercury is toxic and hard to dispose of safely if the thermometer breaks.
Key idea
Celsius, Fahrenheit, and Kelvin
Scale | Unit | Normal body temperature
Kelvin (SI unit)K — 310.15 K
Key idea
The Laboratory Thermometer
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Range
A typical school lab thermometer measures from −10 °C to 110 °C — found from its lowest and highest marked values.
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Correct use
The bulb must not touch the container's bottom or sides. Hold it vertically, and read the temperature while it is still immersed in the liquid, with your eye level with the mark.
Key idea
Working Out the Least Count
The smallest measurable value is found by dividing the gap between two bigger marks by the number of small divisions between them.
Worked exampleIf 10 °C of spread is divided into 10 small divisions, each division measures 10 °C ÷ 10 = 1 °C.
Key idea
Air Temperature
1
Room thermometers
Give an approximate idea of air or room temperature — seen in schools, clinics, and hospitals.
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Weather reports
Report daily maximum and minimum air temperature, which change with the seasons — rising toward summer, falling toward winter.
Key idea
Anna Mani and the Limits of Temperature
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Anna Mani (1918–2001)
The "Weather Woman of India" invented and built many weather-measuring instruments, reducing India's dependence on foreign instruments, and promoted wind and solar energy research.
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How hot, how cold?
The Sun's core reaches about 15 million °C. There's no upper limit to temperature — but there is a lowest possible limit, absolute zero, about −273.15 °C (0 K).
Chapter · Key terms to remember
Key Terms
Temperature
A reliable measure of hotness or coldness.
Thermometer
A device that measures temperature.
Chapter · Key terms to remember
More Key Terms
Kelvin scale
The SI unit of temperature, K.
Clinical thermometer
Measures human body temperature.
Chapter · Key terms to remember
More Key Terms
Laboratory thermometer
Wider-range thermometer for general use.
Air temperature
Temperature of the surrounding atmosphere.
Questions for your notebook
Write these down, then discuss
1The normal temperature of a healthy human is close to: (i) 98.6 °C (ii) 37.0 °C (iii) 32.0 °C (iv) 27.0 °C
237 °C is the same temperature as: (i) 97.4 °F (ii) 97.6 °F (iii) 98.4 °F (iv) 98.6 °F
3Fill in the blanks: (i) The hotness or coldness of a system is determined by its ___. (ii) The temperature of ice-cold water cannot be measured by a ___ thermometer. (iii) The unit of temperature is degree ___.
Project as-is — students copy the questions, then the class discusses answers together.