NCERT Book Class 6 Science Temperature and its Measurement PDF Download

Chapter 7: Temperature and its Measurement

Lambok and his elder sister Phiban live in Shillong. One day they came home from school. Their parents were away at work and Lambok complained that he was feeling feverish. Phiban touched his forehead and felt that he might be having a fever. To confirm this, she took out the thermometer kept in the almirah. She washed its tip with soap and water, and measured Lambok's temperature. To her relief, she found that his temperature was normal. She washed the thermometer tip again, dried it and put it back. She then asked Lambok to change his school uniform, eat his lunch, and rest for some time.

Can it always be correctly judged, that a person has fever, only by touching the person?

7.1 Hot or Cold?

We know from experience that some bodies are hotter than others. For example, during summers, the tap water may be hotter than the cold water from a matka (earthen pot) or a refrigerator. We can realise this by merely touching the two samples of water. But can we always rely upon our sense of touch? Let us find out.

Activity 7.1: Let us investigate

• Take three large containers and label them A, B and C, as shown in Fig. 7.1.
• Pour warm water in container A, tap water in B and ice-cold water in C.
• We will conduct this activity in two parts - prediction and observation.
• Firstly, predict what will you feel if you
  • dip your right hand in A and left hand in C and keep them there for 1-2 minutes.
  • take out your hands from containers A and C, and place both hands simultaneously in B.
• Write down your predictions.
  • What will my right hand feel on dipping it in B?
  • What will my left hand feel on dipping it in B?
• Now, conduct the activity and write your observations.

[Figure 7.1: Feeling hotness or coldness of water by dipping hands, See in your textbook]

Compare whether your observations match with your predictions. Did your right hand feel that the water in container B is cool, while your left hand felt that the same water is warm? What do you infer from these observations?

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

Teacher's Note

This activity shows you that your sense of touch is relative and not absolute. The same water (container B) felt different to each hand because your hands were at different starting temperatures. When measuring temperature in science, you need a thermometer, not your feelings, to get a true and fair answer every time.

7.2 Temperature

A reliable measure of hotness (or coldness) of a body is its temperature. A hotter body has a higher temperature than a colder body. The difference in temperature between the two bodies tells us how hot a body is in comparison to another body. A device that measures temperature is called a thermometer.

There are two kinds of thermometers that you are likely to come across - clinical thermometers and laboratory thermometers. Clinical thermometers are used to measure human body temperatures whereas laboratory thermometers are used for many other purposes. Let us now learn more about thermometers and how to use them to measure temperature.

7.3 Measuring Temperature

7.3.1 Clinical thermometer

You might be familiar with a thermometer, like that shown in Fig. 7.2, which is used for measuring our body temperature. It is called a clinical thermometer. Such thermometers show temperatures digitally. These are also known as digital clinical thermometers and run on batteries. These measure

[Figure 7.2: A digital clinical thermometer, See in your textbook]

Teacher's Note

When using any thermometer, remember that you must wait for the reading to stabilize before you read it. For a digital clinical thermometer, the display will beep or stop changing when the measurement is complete. This is why Phiban in the story waited for the thermometer to give her the correct reading - rushing this step would give you an inaccurate temperature.

Key Points

• Your sense of touch alone cannot reliably tell you how hot or cold something is, because it is relative to your skin temperature.
• Temperature is a reliable measure of how hot or cold a body is, and it is measured using a thermometer.
• A clinical thermometer is used to measure human body temperature and shows the reading on a digital display.

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