Heat

Temperature and Temperature scale

On returning from school, when Ravi touched the iron gate of his house, he found it to be extremely hot. Later, he touched other things made of iron present inside his house and found that they were not hot. Then, he touched other substances (not made of iron) present in his house to determine whether they were hot or cold. He listed the various substances observed in the table given below.

Substances	Hot/ Cold
Tea	Hot
Coffee	Hot
Ice	Cold
Ice cream	Cold
Cooked rice	Hot
Frozen meat	Cold

Try to make a table listing some other substances, which are present in your house and classify them as hot or cold. But how do you decide whether a substance is hot or cold? Can you always tell whether a substance is hot or cold simply by touching it? The following activity will help you understand better.

Measurement of Temperature

Activity:

Take three containers and label them as A, B, and C. Take hot water in container A, and cold water in container C. In container B, mix hot and cold water in equal amounts. Now, place your left hand in container A and right hand in container C for two minutes. Then, dip both your hands in container B.

What can you say about the water present in all three containers? Note your observations in the table given below.

Container	Hot/Cold
A
B
C

What is your observation for container B? Is the water in container B hot or cold?

When you dip your hands in container B, your left hand will tell you that the water is cold, while your right hand will tell you that the water is hot. Thus, you will not be able to distinguish whether the water present in container B is hot or cold.

From this activity, we can conclude that we cannot decide whether a substance is hot or cold just by touching it. Thus, we need something more reliable than our sense of touch to decide whether a substance is hot or cold.

The measure that can be used to detect the degree of hotness and coldness of a substance is called temperature. More the temperature of a substance, the hotter it will be.

Thermometer

The device that is used to measure the temperature is called a therm…