Heat
Science Class Seven
What is Heat?
Heat is a type of energy. Heat relax us in winter while it gives pain in summer days. We always hear about the pain of hot summer days and cold winter days.
An object gets hot after absorbing the heat. Similarly, an object becomes colder by losing of heat. Hot objects can be sensed by touching, but it is never advised to touch anything just to sense how much hot it is. Because one may get his hand burnt by touching a hot object.
Ice is very cold while boiling water is very hot. Summer days are hot while winter days are cold.
There is a question come at this point, "How much hot or how much cold an object is?"
Temperature
Length is measured in inches, feet, millimetre, centimetre, meter, and kilometre etc. Weight is measured in gram, kilogram, etc. Similarly, heat is measured in Celsius or Centigrade, Fahrenheit, or Kelvin.
Similar to length, weight, etc. temperature is a quantity. Heat is measured in term of temperature. It is the temperature which decides how much hot an object is. In other words, hotness or coldness of an object is measured by its temperature.
The unit of temperature is centigrade or Celsius, Kelvin, and Fahrenheit.
Thermometer
Thermometer is an apparatus which is used in measuring of temperature.
The word "Thermometer" is made of two Greek words, "Thermos + Metron". Here "Thermos" means "hot" and "metron" means "measure". This means "measure the hot or hotness". In nutshell, a device which measures the hotness of an object is called "Thermometer".
Invention of Thermometer
Thermometer was not invented by a single scientist, rather modern thermometer came into existence by a series of development processes.
Initially air was started using to show the temperature, later on water, and brandy, etc. are started using to show the temperature.
Daniel Gabriel Fahrenheit invented the first mercury based thermometer in the year of 1714, in which he used mercury to measure the temperature. Daniel Gabriel Fahrenheit was a Dutch scientist.
In the honour of his name, the unit of temperature coined as "Fahrenheit".
Anders Celsius who was Swedish Astronomer suggested another scale "Centigrade" to measure the temperature in 1742.
Later on in his honour the scale for measuring of temperature named as "Celsius".
Structure of Thermometer
Common thermometer is made of a long glass tube with a mercury filled bulb at one end. The tube is calibrated with scale to measure the temperature. In the mid of the glass tube a thin capillary tube is stretched from mercury bulb to almost another end of the glass tube.
Working of Thermometer
The mercury filled in the bulb at one end of thermometer expands and rise in capillary tube and seen as a shining thread after absorbing heat. This shows the degree of temperature up to which scale mercury rises. If thread is not appeared visible, then it can be visible by slightly rotating the thermometer.
Types of Thermometer
There are many types of thermometer. Different types of thermometers are used for different purposes.
Clinical Thermometer
Clinical thermometer is used to measure the human body temperature. It is calibrated with Celsius and/or Fahrenheit scale. It is calibrated from 35o to 42o Celsius. Some thermometer is calibrated from 94o to 108o Fahrenheit. While some of the clinical thermometers are calibrated with both of the scales, i.e. Celsius and Fahrenheit. The Celsius is denoted by letter "C" and Fahrenheit is denoted by letter "F". Because temperature is measured in degree Celsius and/or degree Fahrenheit. Degree Celsius is written as oC and degree Fahrenheit is written as oF in short.
Measuring Body Heat Using Clinical Thermometer
First of all see the temperature observing the shining thread at the scale of thermometer. If it is 36o and above, gently put three to four jerk holding the non-mercury end of the thermometer. After giving two to four gentle jerk, temperature, i.e. shining thread in the long tube of thermometer goes down near about 35o.
Now, put the mercury end of the thermometer under the arm pit or in the mouth. Be careful while keeping the thermometer in the mouth. Do not close your teeth, just hot it using lips and tongue. After one minute remove the thermometer from the armpit or from the mouth where you kept it. Now observe the shining thread of mercury on the measuring scale. Note the temperature.
The normal temperature of human body is 370C. This is read as 37 degree Celsius or 37 degree centigrade. The normal temperature of a person may slightly vary from 370C, it may vary from person to person.
Laboratory Thermometer
There is another type of thermometer which is used in laboratories and called Laboratory Thermometer
In Laboratory Thermometer temperature scale generally starts with -100C and ends at 1100C. It may have more wide range in advance thermometer.
Thermometer which is used to measure the weather temperature is called a maximum-minimum thermometer.
Measuring of Temperature Using Laboratory Thermometer
Laboratory thermometer is used in laboratory to measure the heat of liquids and other many things. If one has to heat a liquid up to 100oC, then the laboratory thermometer is dipped in given liquid. After that liquid is started heating. When mercury level rises up to the 100oC, then heating is stopped.
The mercury level of the laboratory thermometer starts falling down as it is removed from the solution. So, temperature is read while keeping the thermometer in the liquid, temperature of which is to be measured.
Difference between Clinical and Laboratory Thermometer
There is a kink present just above the mercury bulb in the clinical thermometer. It prevents the falling of mercury level on its own, so that temperature can be read easily even after removing the thermometer from mouth or arm pit of a person.
Because of presence of kink above the mercury bulb in the clinical thermometer, it has to be jerked to lower the mercury level.
While in a laboratory thermometer no any kink similar to clinical thermometer is present. The temperature in laboratory is noted while keeping the laboratory thermometer in the hot solution or water. And when a laboratory thermometer removes from the hot solution, the mercury level goes down automatically.
A laboratory thermometer is used to measure the temperature of solution, water, etc. in laboratory.
This is the cause why we do not use a laboratory thermometer to read the temperature of a human body.
Comparison of Celsius and Fahrenheit
Image Reference : By Gringer - n /a, Public Domain, Link
Digital Thermometer
Now a days many advance clinical thermometers are available, such as digital thermometer, infrared thermometer, etc.
In digital thermometer mercury is not used. There is a digital display found on this digital thermometer. The body is temperature is measured using this thermometer by keeping it in mouth or in the armpit. In digital thermometer temperature is displayed in number on digital display.
Digital Thermometer
Infrared Digital Thermometer
The infrared temperature is one of the most modern thermometer.
The body temperature can be measured using laser thermometer by keeping the laser thermometer one to two feet apart from body. And temperature can be read on digital display.
Infrared Thermometer
Maximum-Minimum Thermometer
Maximum-minimum thermometer is used to measure the weather temperature or temperature of a day.
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