NCERT Curiosity · Class 6 · Science
Temperature and its Measurement
Lambok feels feverish. His sister touches his forehead — but touch alone can't really tell us how hot something is.
Thermometers Celsius, Fahrenheit, Kelvin Reading Correctly Anna Mani
Key idea
Touch Alone Can Fool You
Dip one hand in warm water, one in ice-cold water, then both into a bowl of tap water.
Warm-water hand

The same tap water now feels cool to this hand.

Cold-water hand

The same tap water now feels warm to this hand.

Key idea
Temperature and the Thermometer

Temperature

A reliable measure of hotness or coldness. A hotter body has a higher temperature.

Thermometer

A device that measures it — clinical for the body, laboratory for everything else.

Key idea
Clinical Thermometers

Digital

Heat sensors show a reading on a screen. Runs on a battery.

Infrared

Measures body temperature from a distance — used widely during COVID-19.

Mercury · old style

Being phased out — mercury is toxic and hard to dispose of safely.

Key idea
Celsius, Fahrenheit, and Kelvin
Three scales, all describing the same normal body temperature.

Celsius · °C

Normal body temperature: 37.0 °C

Fahrenheit · °F

Normal body temperature: 98.6 °F

Kelvin · K · SI unit

Normal body temperature: 310.15 K

Key idea
The Laboratory Thermometer

Range

A typical school lab thermometer reads from −10 °C to 110 °C.

Correct use

Bulb shouldn't touch the container. Hold it vertical, read at eye level while still immersed.

Key idea
10 °C spread ÷ 10 small divisions = 1 °C per division
The smallest measurable value (the least count) comes from dividing the gap between two bigger marks by the number of small divisions between them.
Key idea
Air Temperature

Room thermometers

Give an approximate idea of air temperature — seen in schools, clinics, and hospitals.

Weather reports

Report daily maximum and minimum air temperature, which rise toward summer and fall toward winter.

Key idea
Anna Mani, the “Weather Woman of India,” built instruments that freed India from relying on foreign ones.
The Sun's core reaches about 15 million °C — there's no upper limit to temperature. But there is a lowest limit: absolute zero, about −273.15 °C (0 K).
1918–2001 Wind & solar research Absolute zero: 0 K
Chapter · key terms to remember
Key Terms

Temperature

A reliable measure of hotness or coldness.

Thermometer

A device that measures temperature.

Celsius scale

Unit °C.

Chapter · key terms to remember
More Key Terms

Fahrenheit scale

Unit °F.

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.

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