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Now users at Ask Physics can add equations to their comments and questions.

Ask Physics has installed the Latex server and now users can type latex code to insert complex equations to their comments or questions.

If you are not familiar with latex code, use the following site to generate the code for the equation that you need.

http://www.codecogs.com/latex/eqneditor.php

When you visit the above site you can edit and view the result of the code generate. You have the option to copy the image of the equation or to copy the code itself (what you typed for getting the image equation; not the html code supplied) and paste the code in your comment.

Go, Try it Now!

Why hole is positive?

Mandeep asks:

“As we take a negative charge on the electron,when
electron leave there position,the left particle is
hole,my question is that why we consider hole as a
positive charge ,as a hole is a efficiency of
electron not containing any charge”

 

Answer: Hole is the deficiency (not efficiency) of an electron. It is assigned a positive charge for the sake of convenience of discussing it like a moving charge. When an electron leaves a site, the atom gets ionized and gets a positive charge. This is actually caused by the deficiency of electron. SO, we treat the vacancy of electron like a mobile positive charge. When an electron from the neighbouring atom leaves its ste and another electron fill a hole previously present, we treat it as if the hole has moved from one site to another.

Links:

• http://britneyspears.ac/physics/basics/basics.htm
• http://ecee.colorado.edu/~bart/book/eband4.htm
• http://hyperphysics.phy-astr.gsu.edu/hbase/solids/intrin.html

Extinguishing fire : Which is better? – Hot water or cold water

“What’s the difference if we add hot water or cold
water to extinguish fire?”

Sreeda asks:

Answer: The thing to be noted here is that the fire extinguishing involves absorption of heat and the absorption of heat in converting hot water to steam is very much more than the heat absorbed in heating cold water to the boiling temperature.  Hot water readily converts to steam absorbing enormous amount of heat and therefore hot water is better for fire extinguishing purpose than cold water.

It is true that cold water absorbs more heat than hot water (say about 1% more than boiling water, but it takes more time than the cooling effect produced by  vaporisation of hot water.