- Our sense of touch is not always a reliable guide to the degree of hotness of an object.
- Temperature is a measure of the degree of hotness of an object.
- Thermometer is a device used for measuring temperatures.
- Different types of thermometers are used for different purposes.
- The thermometer that measures our body temperature is called a clinical thermometer. It consists of a long, narrow, uniform glass tube. It has a bulb at one end. This bulb contains mercury. Outside the bulb, a small shining thread of mercury can be seen. The scale used is the Celsius scale, indicated by °C.
- A clinical thermometer reads temperature from 35°C to 42°C.(India has adopted the Celsius scale and we should read that scale. The other scale with the range 94–108 degrees is the Fahrenheit scale (°F).) The clinical thermometer is designed to measure the temperature of human body only. The temperature of human body normally does not go below 35°C or above 42°C. That is the reason that this thermometer has the range 35°C to 42°C.
- Precautions to be observed while reading a clinical thermometer
- Thermometer should be washed before and after use, preferably with an antiseptic solution.
- Ensure that before use the mercury level is below 35°C.
- Read the thermometer keeping the level of mercury along the line of sight.
- Handle the thermometer with care.
- If it hits against some hard object, it can break.
- Don’t hold the thermometer by the bulb while reading it.
- To measure the temperature of other objects, there are other thermometers. One such thermometer is known as the laboratory thermometer. The range of a laboratory thermometer is generally from –10°C to 110°C.
- The maximum and minimum temperatures of the previous day, reported in weather reports, are measured by a thermometer called the maximum -minimum thermometer.
TRANSFER OF HEAT
- The heat flows from a body at a higher temperature to a body at a lower temperature. There are three ways in which heat can flow from one object to another. These are conduction, convection and radiation.
- 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. In solids, generally, the heat is transferred by the process of conduction.
- The materials which allow heat to pass through them easily are conductors. 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.
- 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.
- All hot bodies radiate heat. When this heat falls on some object, a part of it is reflected, a part is absorbed and a part may be transmitted. The temperature of the object increases due to the absorbed part of the heat.
- Dark-coloured objects absorb radiation better than the light-coloured objects. That is the reason we feel more comfortable in light-coloured clothes in the summer.
- Woolen clothes keep us warm during winter. It is so because wool is a poor conductor of heat and it has air trapped in between the fibers.
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