Monthly Archives: February 2017

Mercury Thermometer -Advantages and Disadvantages

Mercumercury-thermometerry Thermometer is a device used to measure the hotness or coldness of the body. In other words, it is a device to measure body temperature. Mercury Thermometer is very common in labs. Mercury plays major role in the calculation of temperature in this device.

Working Method of Mercury Thermometer:

The lower end of thermometer contains a glass bulb which is full of mercury liquid. The glass bulb is connected to the thin capillary tube in the glass rod. When the thermometer is kept in contact with object or body the temperature increases in the glass bulb of Mercury Thermometer. When temperature increased, the mercury expands in capillary tube.  Though the volume of glass bulb and mercury both increases because of heat. The rate of expansion of mercury is much more greater than that of glass bulb. As the expansion of mercury is high it force to expand in the tube as the temperature increases.

Advantages of Mercury Thermometer:

  • Its boiling point is 357* C and freezing point is -39* C. Therefore, it can be used over a wide range of temperature.
  • Its expansion is nearly uniform over the ordinary range of temperatures. This makes the calibration of the thermometer easier.
  • Mercury can be easily seen through the glass because of its opaque and shining property.
  • It does not wet the glass and can be easily obtained in the pure state.
  • It has low specific heat, so it does not take much heat from the body whose temperature is to be measured.

Disadvantages of Mercury Thermometer:

  • Mercury thermometer cannot measure temperature below -39* C and above 357* C. So, in the Artic and the Antartic region, this thermometer cannot be used.
  • Because of fast expansion, there might not be accurate meter reading.
  • The vapor of Mercury is very poisonous to human beings.


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De Morgan’s Theorem Proof (Both)

De Morgan’s Theorem

A mathematician named DeMorgan developed two theorems in the law of algebraic expression named” De Morgan’s Theorem. It use graphical symbol known as circuit to prove these theorem. These theorems are used in today world for developing many electronic circuit. Every electronic devices are firstly developed by using simple figure in the form of these theorem for input and output. This Theorem is further divided in 2 sub theorem:

  • De Morgan’s First Theorem
  • De Morgan’s Second Theorem

Proof for the both theorems are listed below.

First De Morgan’s Theorem

The De Morgan’s fist theorem states thats, ” The complement of a sum equal to the product of the complements”.

Algebraic expression for the 1st theorem i.e (X+Y)’=X’.Y’


Graphical Symbol:

De Morgan's Theorem (first)

De Morgan's Theorem (Second)




Truth Table:

Inputs Output 1 Output 2
X Y X+Y (X+Y)’ X’ Y’ X’.Y’
0 0 0 1 1 1 1
0 1 1 0 1 0 0
1 0 1 0 0 1 0
1 1 1 0 0 0 0

Comparing the values of (X+Y)’ and X’.Y’ from the truth table, both are equal, hence proved.Conclusion:

Second De Morgan’s  Theorem

De Morgan’s second theorem states , ” The Compliment of a product is equal to the sum of complements”.

Algebraic expression for 2nd theorem i.e (X.Y)’=X’+Y’

Graphical Symbol

De Morgan's Theorem (Second)

Fig: Graphical symbol for De Morgan’s Second Law

Truth Table:

Inputs Output 1 Output 2
X Y XY (XY)’ X’ Y’ X’+Y’
0 0 0 1 1 1 1
0 1 0 1 1 0 1
1 0 0 1 0 1 1
1 1 1 0 0 0 0

By the help of these theorem in we can prove De Morgan’s Theorem. Making or designing software or circuit is very much easier using two theorems.

Conclusion: Comparing the values of (X.Y)’ and X’+Y’ from the truth table both are equal.