SMALLEST BURNS LONGEST | Malayalam
Channel: Arvind Gupta
Date: 2016-04-10

Place three candles in a plate – tall, medium and small height. Light them and cover them with a jar. The tallest candle will extinguish first, followed by the middle on. The smallest will burn the longest. Why? Candle is a hydrocarbon. While burning it consumes oxygen and produces carbon dioxide and water vapor. When the candle uses up the oxygen it extinguishes. So why is it that the smaller candle keeps burning? 
The carbon dioxide produced absorbs most of the heat from the burning candle. Hence the candles push the oxygen down in the jar. So while the longer candle is starved for oxygen the shorter one still can breathe or burn on the pushed colder oxygen. In fact this is the reason why it is advisable to crawl and stay low in case the building catches fire. So even though carbon dioxide is denser than oxygen it stays up because it hotter. This is because of the structure of carbon dioxide molecule. For one molecule of wax burnt 38 molecules of oxygen are burnt and 51 molecules of CO2 and water vapor are produced. So, more gas is produced than the amount of oxygen consumed. In other words, volume of gases inside the jar increases after burning even though the oxygen gets consumed. So water taking space of the burnt oxygen is not the reason for water rising in the jar. Hot carbon dioxide loses its heat to the jar. This reduces the pressure inside the jar and hence water is pulled up. Carbon dioxide absorbing most of the heat is also the reason that in case of fire, it is advised to crawl. 
Thinking time:
What is the percentage of carbon dioxide in jar after all the candles have burnt?
-- Given that fresh air has 20% Oxygen, 78% Nitrogen, .03% Carbon Dioxide, what burns in the candle solid wax, liquid wax or gas wax?
-- Watch our next experiment (Jumping Flame) to see this.

This work is supported by IUCAA (www.iucaa.in) and TATA Trust (www.tata.com/aboutus/sub_index/Tata-trusts)

Credits:,Ashok Rupner, Manish Jain, Pradnya Pujari, Shivaji Mane, Jyoti Hiremath, Arvind Gupta, Vidula Mhaiskar

Dubbed in Malayalam by CK Biju, SNV Sanskrit HSS, Kochi TATA Trust: Education is one of the key focus areas for Tata Trusts, aiming towards enabling access of quality education to the underprivileged population in India. To facilitate quality in teaching and learning of Science education through workshops, capacity building and resource creation, Tata Trusts have been supporting Muktangan Vigyan Shodhika (MVS), IUCAA's Children’s Science Centre, since inception. To know more about other initiatives of Tata Trusts, please visit www.tatatrusts.org