TOPIC 23 OF 46

Hot and Cold — Introducing the Thermometer

🎓 Class 6 Science CBSE Theory Ch 7 — Temperature and Its Measurement ⏱ ~14 min
🌐 Language: [gtranslate]

This MCQ module is based on: Hot and Cold — Introducing the Thermometer

[myaischool_lt_science_assessment grade_level="class_6" science_domain="physics" difficulty="basic"]

Phiban's Fever — A Story from Shillong

It was a misty morning in Shillong. Little Phiban woke up feeling tired and warm. His forehead felt burning hot when his mother touched it with her hand. His elder sister Lambok ran to the cupboard and brought out a thermometer. She placed it under Phiban's arm and waited for a minute. The reading showed 39 °C — that is a high fever!

Lambok quickly called the family doctor. After examining Phiban, the doctor confirmed: "Yes, Phiban has a fever. His body is hotter than normal." The whole family was relieved that Lambok had used a thermometer — because a feeling of warmth on the skin can sometimes trick us. A thermometer tells us the exact number, every time.

Phiban Lambok 39 °C A thermometer gives the exact answer!
Fig 7.1 — Lambok measures Phiban's temperature with a thermometer
Think about it: When you feel warm, how do you decide if you have a real fever or if you just ran too much? Can you trust only your touch?

7.1 Hot or Cold? Can We Trust Our Touch?

Our skin gives us a quick feeling of "hot" or "cold" — but this feeling is not always correct. The same bowl of water can feel cold to one hand and warm to another, if you tricked your hands first! Our sense of touch compares, it does not measure.

Activity 7.1 — The Three Bowls Trick L3 Apply

You need: three bowls, some hot water (not boiling), some ice-cold water, some water at room temperature.

  1. Fill bowl A with warm water, bowl B with cold water, bowl C with water at room temperature.
  2. Dip your left hand in A (warm) and right hand in B (cold) at the same time. Wait one minute.
  3. Now dip both hands together into bowl C (room temperature). What do your two hands tell you?
Predict: Will both hands feel the same temperature in bowl C?
Your left hand (which was in warm water) feels bowl C as cold, while your right hand (which was in cold water) feels bowl C as warm! The water is the same — but your two hands give two different answers. That is why we cannot trust touch to judge temperature.
Warm (A) Cold (B) Room (C) Our touch can trick us!
Fig 7.2 — The three-bowl activity shows that touch is unreliable

7.2 Why We Need a Measuring Device

Knowing "how hot or how cold" matters in many parts of life. We cannot always trust our hands — we need a machine that gives us the exact number. That machine is a thermometer.

🌦️
Weather
To know how hot a summer day is, or how cold a winter morning is.
🍲
Cooking
Boiling milk, baking a cake, or making jam — each needs the right temperature.
🏥
Health
A doctor needs an exact body temperature to diagnose a fever.
🔬
Science
Every experiment in a laboratory records the temperature carefully.
Temperature is a number that tells us how hot or how cold something is. We measure it in degree Celsius (°C) or degree Fahrenheit (°F).

7.3 The Laboratory Thermometer

In science class, we use a special thermometer called the laboratory thermometer. It is a long glass tube that can measure a wide range of temperatures — from very cold to very hot liquids we study in experiments.

Parts of a Laboratory Thermometer

  • Bulb: the round end at the bottom. It holds a liquid — usually coloured kerosene, alcohol, or mercury.
  • Capillary tube: a very thin tube running up the length of the thermometer. The liquid rises and falls here as temperature changes.
  • Scale: markings on the side showing numbers in °C (sometimes also °F).
Range: A laboratory thermometer usually measures from about -10 °C to 110 °C. This is wide enough to measure freezing ice and boiling water.
110 100 80 60 40 20 0 -10 °C Capillary tube Scale (°C) Bulb (with liquid) Freezing point Boiling point
Fig 7.3 — Parts of a laboratory thermometer
Activity 7.4 — Reading the Laboratory Thermometer Correctly L3 Apply

You need: a laboratory thermometer, a beaker of warm water.

  1. Hold the thermometer vertically. Dip the bulb into the water — make sure it does not touch the bottom or sides of the beaker.
  2. Wait till the liquid column stops moving.
  3. Bring your eye exactly level with the top of the liquid column — not above, not below.
  4. Read and note down the number.
Predict: What happens if your eye is above the level of the liquid? Will you read a higher or lower number?
If your eye is above, the reading will look smaller than the true value. If below, it will look bigger. Only when the eye is exactly level (horizontal) with the liquid top is the reading correct. This error is called parallax error.

Rules for Using a Thermometer Safely

Always remember:
  1. Hold the thermometer vertically (straight up).
  2. Dip only the bulb in the liquid — the bulb should not touch the sides or the bottom of the container.
  3. Read with your eye level with the liquid surface.
  4. Do not hold the bulb with your fingers — your body heat will spoil the reading.
  5. Never shake a laboratory thermometer — it is made of thin glass and can break.
CORRECT BULB TOUCHING BOTTOM ✗ TILTED ✗
Fig 7.4 — Correct and wrong ways to use a thermometer
Activity 7.5 — Measure the Temperature of Warm Water L3 Apply

You need: a beaker of warm water, a laboratory thermometer, a stand or clamp.

  1. Clamp the thermometer so the bulb is fully inside the water but not touching the glass.
  2. Wait about 30 seconds.
  3. Read the value at eye-level. Note it in your notebook.
  4. Pour in a little more hot water. Take the reading again. Did the number go up?
Predict: If you add ice-cold water, will the reading rise or fall?
Adding cold water makes the mixture cooler — the liquid column in the capillary tube will drop, and the reading will go down. Adding hot water makes the liquid expand and rise, so the reading goes up.

Celsius and Fahrenheit — Two Popular Scales

The scale used most often in India and in science is the Celsius scale (°C). In some countries like the USA, people use the Fahrenheit scale (°F). Both measure the same thing, just with different numbers.

EventCelsius (°C)Fahrenheit (°F)
Water freezes (ice forms)0 °C32 °F
Room temperature (a nice day)25 °C77 °F
Normal body temperature37 °C98.6 °F
Water boils100 °C212 °F

Interactive: Read the Thermometer L3

Look at the thermometer below. What temperature does it show?
100 75 50 25 0 °C

Hint: The liquid top is between 25 and 50. Look carefully at where it stops.

Competency-Based Questions

Phiban's class goes on a science trip. Their teacher gives each group a laboratory thermometer and three cups of water: cup P (just boiled, very hot), cup Q (a little warm), cup R (with ice). The class has to record the temperature of each cup correctly.

Q1. What is a thermometer? L1

A thermometer is a device used to measure the temperature of a body or a substance. The reading is usually given in degree Celsius (°C).

Q2. Which of these is the correct way to hold a laboratory thermometer? L2

  • A. Horizontally, bulb touching the bottom of the beaker
  • B. Vertically, bulb fully in liquid but not touching bottom/sides
  • C. Tilted at 45° with bulb hanging out of the liquid
  • D. Hold the bulb with fingers to keep it steady
Answer: B. The bulb must be fully immersed but not touching the container, and the thermometer must be upright. Fingers on the bulb would warm it and spoil the reading.

Q3. Why can't we use only our hands to decide how hot or cold water is? L2

Our sense of touch compares — it tells us hotter or colder than our skin. After holding something warm, lukewarm water feels cold; after holding something cold, the same water feels warm. Touch gives a relative answer, not an exact number.

Q4. On the Celsius scale, at what temperature does water freeze and at what temperature does it boil? L1

Water freezes at 0 °C and boils at 100 °C (at normal sea-level conditions).

Q5. In the science trip, one student holds the thermometer by its bulb while reading cup Q. What will go wrong? L4

The heat of the student's hand will flow into the bulb and raise the liquid level. The reading will show a temperature higher than cup Q's real temperature — a wrong result.

Assertion – Reason

Assertion (A): A thermometer is needed to measure temperature exactly.

Reason (R): Our hands give the same answer to every person every time.

  • A. Both A and R are true, R explains A.
  • B. Both true, R does not explain A.
  • C. A true, R false.
  • D. A false, R true.
Answer: C. A is correct, but R is false — our hands give different answers depending on what they were doing before.

Assertion (A): While reading a thermometer, the eye should be at the same level as the top of the liquid.

Reason (R): Reading from above or below causes an error called parallax error.

  • A. Both A and R are true, R explains A.
  • B. Both true, R does not explain A.
  • C. A true, R false.
  • D. A false, R true.
Answer: A. Both are true and the reason correctly explains why we keep our eye level with the liquid.

Assertion (A): A laboratory thermometer can measure the temperature of a human body accurately.

Reason (R): The laboratory thermometer has a very wide range (about -10 °C to 110 °C).

  • A. Both A and R are true, R explains A.
  • B. Both true, R does not explain A.
  • C. A true, R false.
  • D. A false, R true.
Answer: D. A is false — a laboratory thermometer is not used on the human body; we use a clinical thermometer. R is correct (the wide range is true).

Next → Part 2: Clinical Thermometer & Body Temperature

Frequently Asked Questions — Hot and Cold — Introducing the Thermometer

What does the topic 'Hot and Cold — Introducing the Thermometer' cover in Class 6 Science?

The topic 'Hot and Cold — Introducing the Thermometer' is part of NCERT Class 6 Science Chapter 7 — Temperature and its Measurement. It covers the key ideas of hot, cold, temperature, thermometer, mercury, Celsius scale, sense of touch, explained through everyday examples, labelled diagrams and hands-on activities from the NCERT Curiosity textbook. Class 6 students learn simple definitions, see why each idea matters in daily life, and try short experiments and observations. The lesson uses easy language, colourful pictures and small questions so that young learners build a strong base for higher classes and for competency-based questions in CBSE school tests.

Why is 'Hot and Cold — Introducing the Thermometer' important for Class 6 NCERT Science?

'Hot and Cold — Introducing the Thermometer' is important because it builds the first ideas of science that Class 6 students will use again in Class 7, 8 and beyond. NCERT Chapter 7 — Temperature and its Measurement — introduces hot and connects it to things children already see at home, at school and in nature. Learning this topic helps students ask better questions, understand simple news about science, and score well in CBSE tests that use competency-based questions. The chapter also supports NEP 2020 by encouraging curiosity, observation and learning by doing rather than only reading and memorising.

What are the key ideas students should remember from Hot and Cold — Introducing the Thermometer?

The key ideas in 'Hot and Cold — Introducing the Thermometer' for Class 6 Science are: hot, cold, temperature, thermometer, mercury, Celsius scale, sense of touch. Students should be able to say each term in their own words, give one or two easy examples from daily life, and draw a small labelled diagram where needed. A good way to revise is to make flashcards, write a short note in the science notebook, and solve the NCERT in-text and exercise questions of Chapter 7. Linking every idea to something seen at home or school — in the kitchen, garden, playground or sky — makes these ideas easy to remember for unit tests and the annual CBSE examination.

How is Hot and Cold — Introducing the Thermometer taught using activities in NCERT Curiosity Class 6?

NCERT Curiosity Class 6 Science teaches 'Hot and Cold — Introducing the Thermometer' through an inquiry-based approach using Predict–Observe–Explain activities. Students first make a guess, then try a small experiment with safe, easily available materials, and finally explain what happened and why. This matches the NEP 2020 focus on learning by doing. For Chapter 7 — Temperature and its Measurement — the textbook has hands-on tasks, labelled pictures and thinking questions built for Bloom's Taxonomy Levels 1 to 6. Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding instead of only rote learning.

What real-life examples of hot can Class 6 students see at home?

Class 6 students can see hot at home in many simple ways linked to 'Hot and Cold — Introducing the Thermometer'. Kitchens, school bags, playgrounds, the garden and the night sky are full of examples that match NCERT Chapter 7 — Temperature and its Measurement. For example, students can look at food labels, watch changes while cooking, try safe activities with water, magnets or shadows, and observe the Sun, Moon and weather each day. Keeping a small science diary — with the date, what was observed and a quick drawing — turns daily life into a mini science lab. These real-life links make concepts easy to remember and help in answering competency-based questions in CBSE Class 6 Science.

How does 'Hot and Cold — Introducing the Thermometer' connect to other chapters of Class 6 Science?

'Hot and Cold — Introducing the Thermometer' connects to many other chapters in NCERT Class 6 Science Curiosity. The ideas of hot come back when students study related topics like diversity in the living world, food, magnets, measurement, materials, temperature, water, separation, habitats, natural resources and the solar system. For example, what students learn here helps them build mental pictures for later chapters and for Class 7 and Class 8 Science. Teachers often ask cross-chapter questions in CBSE exams to check if students can use what they learned in Chapter 7 — Temperature and its Measurement — in new situations. This linked approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.

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