In our day-to-day life, we come across a number of objects. Some of them are hot and some of them are cold. Tea is hot and ice is cold.
A reliable measure of the hotness of an object is its temperature. Temperature is measured by a device called thermometer.
The thermometer that measures our body temperature is called a clinical thermometer.
A clinical thermometer consists of a long, narrow, uniform glass tube. It has a bulb at one end. This bulb contain-s mercury. Outside the bulb, a small shining thread of mercury can be seen.
A clinical thermometer reads temperature from 35°C to 42°C.
Reading a thermometer
The temperature should always be stated with its unit, °C.
The normal temperature of human body is 37°C. Note that the temperature is stated with its unit.
The temperature of every person may not be 37°C.
The clinical thermometer is designed to measure the temperature of human body only. The temperature of human body normally does not go below 35oC or above 42oC. That is the reason that this thermometer has the range 35oC to 42oC.
When we measure the temperature of other objects such thermometer is known as the laboratory thermometer. The range of a laboratory thermometer is generally from −10°C to 110°C.
While we take a frying pan on the flam, we observed that a frying pan becomes hot when kept on a flame. It is because the heat passes from the flame to the utensil. When the pan is removed from the fire, it slowly cools down.
So the heat is transferred from the pan to the surroundings. The heat flows from a hotter object to a colder object. The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.
The materials which allow heat to pass through them easily are conductors of heat. For examples, aluminum, iron and copper.
The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators.
The water and air are poor conductors of heat.
The air from the sea is called the sea breeze. To receive the cooler sea breeze, the windows of the houses in coastal areas are made to face the sea. At night it is exactly the reverse. The water cools down more slowly than the land. So, the cool air from the land moves towards the sea. This is called the land breeze.
From the sun the heat comes to us by another process known as radiation. The transfer of heat by radiation does not require any medium. It can take place whether a medium is present or not.
In summer we prefer light-coloured clothes and in winter we usually wear dark-coloured clothes.
Woollen clothes keep us warm in winter
In the winter, we use woollen clothes. Because of wool is a poor conductor of heat. Moreover, there is air trapped in between the wool fibres.