HEAT

IMPORTANT TERMS

Thermometer               A device that is used to measure temperature.

Joule                           The SI unit of heat is Joule (J).

Conductors                  Substances that allow heat to pass through them. E.g. Aluminium

Insulators                     Substances that do not allow heat to pass through them. E.g. Wood

Sea Breeze                  The wind blowing from sea towards land that develops over water bodies

Land Breeze                The cool air that moves from the land towards the sea.

 

 

TEMPERATURE

Temperature is used to measure how hot or cold an object is. It is a measure of hotness or coldness of an object.

MEASURING TEMPERATURE

Temperature is measured by a device called thermometer. Mercury and alcohol are commonly used liquids in thermometers. These liquids expand when they warm up and contract when they cool down.

TYPES OF THERMOMETERS

Thermometers are of various types:

A clinical thermometer consists of long glass tube, which has a bulb at one end. This bulb contains mercury. It is used to measure the temperature of the body. So, a person suffering from fever will need a clinical thermometer to measure his temperature. The range of this thermometer is from 35⁰C to 42⁰C.

Laboratory thermometer is used to measure the temperature of hot solids and liquids during experiments. It can also be used to measure the room temperature.

The range of temperatures that a laboratory thermometer can measure is generally from -10⁰C to 100⁰C.

The Maximum-minimum thermometer records the highest and lowest temperatures since it was last set.

Nowadays, digital thermometers are used to measure temperature which do not use mercury. The temperature is displayed as a number, which makes it easy to read.

Daniel Gabriel Fahrenheit, a German physicist invented the first mercury thermometer in 1714. He also invented the alcohol thermometer.

SCALES OF TEMPERATURE

There are three scales that are used to measure temperature: Celsius, Fahrenheit and Kelvin.

The Celsius scale is commonly used to measure temperature. It is indicated by the symbol of ⁰C.

Anders Celsius who was an astronomer, invented the Celsius temperature scale.

The Fahrenheit scale is used to measure temperature. It is indicated by the symbol of ⁰F.

The Kelvin scale is a temperature scale that is used for scientific purposes. It is different from the other two scales as it has an absolute zero below which temperature scale do not exist. The Kelvin scale is indicated by the symbol of K.

William Thomson, also known as Lord Kelvin invented the Kelvin Scale.

To create a standard scale to measure temperature, there are two fixed temperatures that are used. The temperature of melting point of ice is taken as the lower fixed point and the boiling point of water is taken as the upper fixed point.

TRANSFER OF HEAT

Heat is a form of energy that can be transferred from one object to another.

Heat energy always flows from a region of higher temperature to a region of lower temperature.

There are three main ways through which heat energy can be transferred: conduction, convection and radiation.

Conduction

Conduction is the process by which heat is transferred from one molecule to another without the actual movement of molecules from one place to another.

The conduction of heat is effective when the molecules are closely packed together.

The particles in solids are closely packed and cannot move freely. Therefore, in solids, the process of heat transfer takes place through conduction.

There are different materials to conduct heat. The materials which conduct heat easily are called good conductors of heat. E.g. aluminum, iron and copper.

The materials that conduct heat poorly are called insulators. E.g. wood, glass and plastic.

Convection

Convection is the process by which heat is transferred in liquids and gases by the actual movement of molecules. The process of convection takes place in both liquids and gases as the molecules are far apart from each other and can move freely.

Convection plays a primary role in maintaining a moderate temperature in coastal areas. Land breeze and sea breeze are the examples of convection and play an important role in maintaining a moderate temperature in coastal areas.

Radiation

Radiation is a mode of heat transfer from one body to another without the help of any medium and without heating the medium through which it passes.

In this mode, the heat energy travels in the form of electromagnetic waves.

E.g. Heat of the Sun travels long distances in vacuum and reaches the Earth through the process of radiation.

 

INTERESTING FACTS

 

• Most of the countries in the world use Celsius scale to measure temperature.
• The temperature of human body gets affected by age. It has been studied that with advancing age, the average body temperature gets lower.
• The skin of a polar bear is black, which helps it to absorb more heat from the sun.