Combustion and flame Worksheet-7

Combustion and flame Worksheet-7

 

  1. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?

 

  1. Is the food a fuel for our body?

 

  1. Can you burn paper when a burning matchstick is brought near it? Why?

 

  1. Why do different substances catch fire at different temperatures?

 

  1. Why is water poured to extinguish burning wood?

 

  1. Can you put off a fire due to electric short circuit by using water? Why?

 

  1. How is fire extinguished at airports and petrol pumps?

 

  1. Which substances burn with a flame?

 

  1. Which zones of the candle flame have the maximum and minimum temperature?

 

  1. Hydrogen has the highest calorific value, but it is not used as a fuel. Why?

 

  1. Why do the goldsmiths use the outermost zone of the flame?

 

Answer:

  1. Ramesh’s water beaker will be heated in a shorter span of time because the outermost part of the flame is hottest. Complete combustion of fuel takes place producing maximum heat energy. The yellow part of the flame is less hot due to incomplete combustion of fuel.

 

  1. Yes food acts as fuel for our body. Carbohydrate, fat, protein present in the food get oxidise (react with oxygen) producing energy.

 

  1. Yes paper can be burnt when a burning matchstick is brought near it as the heat produced by burning matchstick increases the temperature of paper reaching its ignition temperature.

 

  1. Different substances catch fire at different temperatures because their ignition temperature varies.

 

  1. Water evaporates taking off heat from the burning wood thus decreasing its temperature below ignition temperature.

 

  1. Fire caused due to electric short circuit cannot be extinguished by using water because water conducts electricity posing danger to the person extinguishing fire.

 

  1. Fire at airports and petrol pumps can be extinguished by using fire extinguishers.

Carbon dioxide fire extinguisher

This type of fire extinguisher consists of carbon dioxide filled under high pressure in cylinders.

Carbon Dioxide fire extinguishers are filled with non-flammable carbon dioxide gas under extreme pressure. The pressure in the cylinder is so high that when it is used, bits of dry ice may shoot out the horn. CO2 fire extinguishers are useful for flammable liquid and electrical fires only.

Carbon dioxide extinguishes fire by forming a blanket over fire thus cutting off the supply of oxygen. The carbon dioxide is also very cold as it comes out of the extinguisher, so it cools the fuel as well.

 

  1. The substances which vapourise burn with flame.

 

  1. The outer zone (blue) is the hottest part of the flame.

The inner zone (black) is the coolest part of the flame.

 

  1. Hydrogen has the highest calorific value so it may be considered as the best fuel but it is not used because it is highly inflammable, its transport, storage and handling are difficult.

 

  1. Outermost zone of a flame is the hottest hence goldsmiths use the outermost zone of the flame