Science · Class 6 · Chapter 7

Temperature and its Measurement

• Temperature — A reliable measure of hotness or coldness.
• Thermometer — A device that measures temperature.
• Celsius scale — Unit °C.
• Fahrenheit scale — Unit °F.
• Kelvin scale — The SI unit of temperature, K.
• Clinical thermometer — Measures human body temperature.
• Laboratory thermometer — Wider-range thermometer for general use.
• Air temperature — Temperature of the surrounding atmosphere.

Chapter 7 · Concept 1 of 8

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.
• What happens — 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.
• The conclusion — We cannot always rely on our sense of touch to correctly judge how hot or cold something really is.

Chapter 7 · Concept 2 of 8

Temperature and the Thermometer

• Temperature — A reliable measure of the hotness or coldness of a body. A hotter body has a higher temperature than a colder one.
• Thermometer — A device that measures temperature. Clinical thermometers measure body temperature; laboratory thermometers are used for many other purposes.

Chapter 7 · Concept 3 of 8

Clinical Thermometers

• Digital — Uses heat sensors and shows a reading on a screen. Runs on a battery.
• Infrared — Measures body temperature from a distance without touching — used widely during COVID-19.
• Mercury (old style) — Being phased out — mercury is toxic and hard to dispose of safely if the thermometer breaks.

Chapter 7 · Concept 4 of 8

Celsius, Fahrenheit, and Kelvin

• Scale | Unit | Normal body temperature
• Celsius — °C — 37.0 °C
• Fahrenheit — °F — 98.6 °F
• Kelvin (SI unit) — K — 310.15 K

Chapter 7 · Concept 5 of 8

The Laboratory Thermometer

• Range — A typical school lab thermometer measures from −10 °C to 110 °C — found from its lowest and highest marked values.
• 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.

Chapter 7 · Concept 6 of 8

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 example — If 10 °C of spread is divided into 10 small divisions, each division measures 10 °C ÷ 10 = 1 °C.

Chapter 7 · Concept 7 of 8

Air Temperature

• Room thermometers — Give an approximate idea of air or room temperature — seen in schools, clinics, and hospitals.
• Weather reports — Report daily maximum and minimum air temperature, which change with the seasons — rising toward summer, falling toward winter.

Chapter 7 · Concept 8 of 8

Anna Mani and the Limits of Temperature

• 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.
• 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).

Quick Recap

Check Your Understanding

1. 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
2. 237 °C is the same temperature as: (i) 97.4 °F (ii) 97.6 °F (iii) 98.4 °F (iv) 98.6 °F
3. 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 ___.