Chapter 7
🌡️ Temperature and its Measurement
Curiosity | NCERT Grade 6 Science
📚 Table of Contents
📷 Testing hotness/coldness of water using hands in three containers
👋 7.1 Hot or Cold? — Limits of Touch
We naturally sense temperature through touch — we know when something is hot or cold. But can we always trust our sense of touch?
🧪 The Three-Container Experiment
If you put your right hand in warm water and left hand in cold water for 1-2 minutes, then put BOTH hands in room-temperature water — your right hand feels COLD but your left feels WARM! Same water, opposite feelings! This shows our sense of touch is unreliable for measuring temperature accurately. ⚠️ Important Conclusion
We CANNOT always rely on our sense of touch to judge accurately whether a body is hot or cold. We need a reliable measuring device — a thermometer! 🌡️ 7.2 What is Temperature?
📖 Definition
Temperature is the reliable measure of hotness or coldness of a body. A hotter body has a higher temperature; a colder body has a lower temperature. 🌡️ Thermometer
A thermometer is a device used to measure temperature. Different types exist for different purposes. | Scale | Unit | Symbol | Used For |
|---|---|---|---|
| Celsius | degree Celsius | °C | Most common, used in India |
| Fahrenheit | degree Fahrenheit | °F | Used in USA, body temp |
| Kelvin | Kelvin | K | Scientific purposes, SI unit |
Normal body temperature = 37.0°C = 98.6°F
🏥 7.3 Clinical Thermometer
📖 Clinical Thermometer
A clinical thermometer is used to measure human body temperature. It is the type your doctor or family uses when checking for fever. 
📷 Digital clinical thermometer
Types of clinical thermometers:
- Digital clinical thermometer — Shows temperature as a number on display; runs on battery; safe (no mercury)
- Mercury thermometer (old) — Glass tube with mercury; mercury is toxic and dangerous if broken → no longer recommended
How to use a digital clinical thermometer:
1
Wash the tip with soap and water before use
2
Place the tip under the tongue, in the armpit, or on forehead as instructed
3
Wait for the beep signal
4
Read the temperature shown on the display
5
Wash the tip again and store properly
Normal human body temperature = 37.0°C (98.6°F). A temperature higher than this indicates fever. Body temperature varies slightly by individual and time of day.
🔬 7.4 Laboratory Thermometer
📖 Laboratory Thermometer
A laboratory thermometer is used to measure temperatures of liquids and substances in experiments. It has a wider range than a clinical thermometer. | Feature | Clinical Thermometer | Laboratory Thermometer |
|---|---|---|
| Purpose | Body temperature | Experiments, liquids |
| Range | ~35°C to 42°C | −10°C to 110°C (wider) |
| Kink | Has a kink (holds reading) | No kink |
| Use position | Held in place on body | Held in hand in substance |
💡 The kink (bend) in a mercury clinical thermometer prevents mercury from falling back when removed — allowing the doctor to read it calmly!
📷 Laboratory thermometer used for experiments
🌤️ 7.5 Air Temperature & Weather
The temperature of the air around us — atmospheric temperature — changes throughout the day and across seasons.
- Air temperature is measured with a thermometer placed in shade (direct sunlight gives wrong reading)
- Maximum temperature of the day is usually around 2–3 pm
- Minimum temperature is usually just before sunrise
- Weather stations record temperature to prepare weather forecasts
📝 Chapter Summary
- Sense of touch is unreliable for measuring temperature accurately
- Temperature = reliable measure of hotness/coldness; measured in °C or °F
- Normal human body temperature = 37°C = 98.6°F
- Clinical thermometer: measures body temp (35-42°C), has a kink
- Digital thermometers are safe; mercury ones are toxic
- Laboratory thermometer: wider range (−10 to 110°C), used in experiments
- Air temperature measured in shade; varies through the day
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