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Temperature and its Measurement – Class 6 Science Chapter 7 Notes & NCERT PDF

Class 6ScienceChapter 7NCERT book: Curiosity - Science Class 6

Notes and a simple summary of Chapter 7 of the NCERT Class 6 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 7: Temperature and its Measurement

Introduction

"Wrong measurements are worse than no measurements at all." — Anna Mani

Lambok and his elder sister Phiban live in Shillong. Lambok comes home from school feeling feverish. Phiban touches his forehead and thinks he may have fever — but to be sure, she takes out the thermometer, washes its tip with soap and water, measures his temperature, finds it normal, washes and dries the tip again and puts it back. This shows two things: touch alone is not reliable, and thermometers must be used carefully and hygienically.

Key Concepts

7.1 Hot or cold?

Can we judge hotness by touch? Activity 7.1 answers this with three containers: A – warm water, B – tap water, C – ice-cold water. Keep the right hand in A and the left in C for 1–2 minutes, then put both in B. The right hand feels B as cool and the left hand feels B as warm — the same water feels different!

We cannot always rely on our sense of touch to decide correctly whether a body is hot or cold.

7.2 Temperature

Temperature is a reliable measure of the hotness or coldness of a body. A hotter body has a higher temperature. A device that measures temperature is a thermometer.

Two common kinds: clinical thermometers (human body temperature) and laboratory thermometers (other purposes).

7.3.1 Clinical thermometer

  • Modern clinical thermometers are digital, run on batteries and use heat sensors.
  • Mercury thermometers are being replaced because mercury is extremely toxic and hard to dispose of if the thermometer breaks.
  • Infrared (non-contact) thermometers, used widely during COVID-19, measure temperature from a distance and reduce the spread of disease.

    • Steps (Activity 7.2): wash hands and the tip → press reset → place under the tongue and close the mouth → wait for the beep/flash → read the display → record → clean and dry the tip.

    Precautions: read the manual; wash the tip before and after use; keep the display out of water; don't hold it by the tip.

    Normal body temperature

  • Taken as 37.0 °C (= 98.6 °F). It is an average of many healthy people — a healthy person may be slightly above or below.
  • Body temperature depends on age, time of day and activity level.
  • Human temperature normally stays between 35 °C and 42 °C — this is why a clinical thermometer has a small range and cannot measure boiling water or ice.
  • For small children and elderly people, the thermometer can be kept in the armpit; the reading is about 0.5 °C to 1 °C lower than actual body temperature.

    • Temperature scales

  • Celsius scale – unit degree Celsius (°C) – used by clinical and lab thermometers.
  • Fahrenheit scale – unit degree Fahrenheit (°F) – not used much in science now.
  • Kelvin scale – unit kelvin (K) – SI unit of temperature.
  • All three scales are named after the scientists who developed them.
    • Temperature in kelvin = Temperature in °C + 273.15

    Worked example: 37 °C = 37 + 273.15 = 310.15 K. Water boiling at 100 °C = 373.15 K. Absolute zero, the lowest possible temperature, is −273.15 °C = 0 K.

    Writing rules: scale names start with a capital letter (Celsius scale); "degree" is lowercase; "kelvin" is lowercase; symbols °C, °F, K are capitals; no degree sign with K; leave a space: "37.0 °C".

    Before thermometers, pulse rate was used in India to detect fever — but pulse is affected by other things, so it is not reliable alone.

    7.3.2 Laboratory thermometer

  • A long, narrow, uniform, sealed glass tube with a bulb containing liquid — usually alcohol coloured red or mercury.
  • The liquid column rises or falls with temperature; the Celsius mark at the top of the column is the reading.
  • Typical range: −10 °C to 110 °C.

    • Finding the smallest value (Activity 7.4): between 0 °C and 10 °C there are 10 small divisions, so one division = 10 °C ÷ 10 = 1 °C.

    Worked example (Exercise 12): 50 divisions between 0 °C and 100 °C → each division = 100 ÷ 50 = 2 °C.

    Correct way to use it

  • Bulb must not touch the bottom or sides of the beaker.
  • Hold the thermometer vertical, not tilted.
  • Read while it is still immersed — the column starts falling as soon as you remove it.
  • Keep your eye in line with the top of the liquid column.
  • Precautions: handle with care; do not hold it by the bulb.

    • A lab thermometer is not used for body temperature — its reading falls as soon as it is taken out of the mouth, and it is not designed for that use.

    Ice and boiling water (teacher demo): temperature stays constant while ice melts and constant while water boils.

    Activity 7.6: Phiban's class in Shillong recorded boiling water at 97.8, 98.0, 97.9, 98.0, 98.1 °C. Small differences can come from not reading the thermometer correctly (eye position, tilting, bulb touching the beaker).

    7.3.3 Air temperature

  • Room thermometers on walls give approximate room temperature.
  • Weather reports give maximum and minimum air temperature of the day; these vary daily and rise towards summer and fall in winter.
  • Air temperature data from weather stations is used for weather forecasts.
    • Anna Mani (1918–2001), the "Weather Woman of India", built many weather instruments in India, reducing dependence on other nations, and explored wind and solar energy.

    Activities in the Chapter

  • 7.1 Let us investigate: three-container hot/cold touch test → touch is unreliable.
  • 7.2 Let us measure: measure body temperatures of 10 friends with a digital thermometer (Table 7.1).
  • 7.3 Let us observe: find the range of a lab thermometer.
  • 7.4 Let us observe and calculate: find the smallest division.
  • 7.5 Let us measure: temperature of warm water; column falls when taken out.
  • 7.6 Let us compare: boiling-water readings of different students.
  • 7.7 Let us analyse: record max/min air temperatures for 10 days.

    • Key Terms

  • Temperature (ताप/तापमान) – measure of hotness or coldness
  • Thermometer (तापमापी)
  • Clinical thermometer (डॉक्टरी थर्मामीटर)
  • Laboratory thermometer (प्रयोगशाला तापमापी)
  • Celsius scale / degree Celsius (सेल्सियस पैमाना) – °C
  • Fahrenheit scale (फ़ारेनहाइट पैमाना) – °F
  • Kelvin scale / kelvin (केल्विन) – K, SI unit
  • Range (परास) – lowest to highest temperature a thermometer can measure
  • Absolute zero (परम शून्य) – −273.15 °C or 0 K
  • Maximum/Minimum air temperature (अधिकतम/न्यूनतम वायु तापमान)
  • Infrared thermometer (अवरक्त तापमापी)

    • Real-life Connections

  • Parents track fever with a digital thermometer (like Vaishnavi's record in Exercise 9).
  • Airports and hospitals use infrared thermometers.
  • Weather forecasts on TV use max/min temperatures.
  • Mercury thermometers are being phased out for safety.

    • Common Misconceptions

  • "Touching the forehead is enough to detect fever." — Touch can mislead (Activity 7.1).
  • "Normal temperature must be exactly 37.0 °C." — 37.0 °C is an average; small variations are normal.
  • "A clinical thermometer can measure boiling water." — Its range is only about 35–42 °C.
  • "Write 300 °K." — Kelvin never uses the degree sign: 300 K.
  • "A fever of 101 degrees means 101 °C." — That is on the Fahrenheit scale (Exercise 14); 101 °C would be impossible for a human.

    • Keep the Curiosity Alive (Exercise Hints)

  • Ex. 1–2: Normal temperature ≈ 37.0 °C = 98.6 °F.
  • Ex. 4: Lab thermometer range is usually −10 °C to 110 °C.
  • Ex. 9 (Vaishnavi): highest = 40.0 °C, Day One at 7 pm; temperature returned to normal on Day Three.
  • Ex. 10: To measure 22.5 °C choose a thermometer whose smallest division is 0.5 °C.
  • Ex. 12: 50 divisions for 100 °C → 2 °C per division.

    • 💡 Key Learning Points

    • ✓Our sense of touch is unreliable; temperature measured with a thermometer tells us correctly how hot or cold a body is.
    • ✓Clinical (digital) thermometers measure body temperature; normal is taken as 37.0 °C (98.6 °F), an average value.
    • ✓The three scales are Celsius (°C), Fahrenheit (°F) and Kelvin (K); kelvin is the SI unit and K = °C + 273.15.
    • ✓A laboratory thermometer (range typically −10 °C to 110 °C) must be held vertically, bulb not touching the beaker, and read while immersed with the eye level to the column.
    • ✓Find the smallest value a thermometer reads by dividing the temperature gap between two big marks by the number of divisions.

    👨‍🏫 Teaching Tips

    • →Run Activity 7.1 live with three buckets — let students predict first, then feel; the surprise makes the concept stick.
    • →Demonstrate the digital thermometer hygiene routine step by step and have students repeat it in pairs.
    • →Give students printed thermometer scale images and ask them to find range and smallest division before using a real one.
    • →Show a lab thermometer being removed from warm water so students see the column fall immediately.
    • →Display the class's boiling-water readings (like Table 7.2) and discuss why they differ.
    • →Assign a 10-day max/min temperature log from newspapers and plot it on a simple graph.
    • →Tell the story of Anna Mani to connect measurement with Indian scientists and self-reliance.
    • →Practise conversions with a quick 'Celsius to kelvin' relay race on the board.

    📋 Assessment Questions

    1. Can the student explain why the same tap water felt warm to one hand and cool to the other?
    2. Can the student list the steps and precautions for using a digital clinical thermometer?
    3. Can the student convert a Celsius temperature to kelvin and write it with the correct symbol?
    4. Can the student find the range and smallest division of a given lab thermometer?
    5. Can the student identify the correct way of reading a lab thermometer from diagrams of four students?

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    Keep learning

    All chapters in Curiosity - Science Class 6

    1. 1. The Wonderful World of Science
    2. 2. Diversity in the Living World
    3. 3. Mindful Eating: A Path to a Healthy Body
    4. 4. Exploring Magnets
    5. 5. Measurement of Length and Motion
    6. 6. Materials Around Us
    7. 7. Temperature and its Measurement
    8. 8. A Journey through States of Water
    9. 9. Methods of Separation in Everyday Life
    10. 10. Living Creatures: Exploring their Characteristics
    11. 11. Nature’s Treasures
    12. 12. Beyond Earth