Science Class 8 : Fuel Fire and Flame

                                       Fuel, Fire and Flame

Q1. You are provided with three watch glasses containing milk,petrol and mustard oil, respectively. Suppose you bring a burning candle near these materials one by one, which material(s) will catch fire instantly and why?

Ans. Petrol will catch fire instantly because it is highly inflammable and its ignition temperature is very less as compared to other substance. Ignition temperature is the lowest temperature at which the substance catches fire.

Q2. What are the essential requirements to produce fire? How fire extinguisher is useful for controlling fire.

Ans. Three essential requirements.

a. Fuel

b. Air

c. Heat to acquire the ignition temperature.

Flames need fuel oxygen and heat in order to burn. Fire extinguishers are designed to remove one of these elements by applying an agent that either cools the burning fuel, or removes or displaces the surrounding oxygen.

Q3. Give two examples each for a solid, liquid and gaseous fuel along with some important uses.

Ans. Types of fuels

Solid fuel - Coal, wood, etc

Liquid fuel - Kerosene, petrol, diesel etc.

Gaseous fuel -  CNG, PNG, LPG etc.

Uses

Coal - coal has been used as an energy resource, primarily burned for the production of electricity and heat, and is also used for industrial purposes, such as refining metals.

Wood -  Wood fuel can be used for cooking and heating,and occasionally for fueling steam engines and steam turbines that generate electricity.

Kerosene oil -  Fuel for stoves, lamps etc.

Petrol - For running vehicles

LPG-  Fuel for industry etc.

Q4 The calorific value of petrol and CNG are 45000KJ/kg and 50000KJ/kg, respectively. If you have vehicle which can run on petrol as well as CNG, which fuel will you prefer and why?

Ans.  CNG, because the calorific value of CNG is higher than that of petrol. Therefore, CNG will be more economical. At the same time, it produces the least air pollutants.

Q5. Although wood has a very high calorific value, we still discourage its use as a fuel. Explain.

Ans. 1. Burning of wood produces lot of air pollution.

2. Use of wood as fuel encourages cutting of trees leading to deforestation.

Q6. Forest fire produces a lot of air pollution. Write in brief about the reasons of forest fires.

Ans. Forest fire always start because of two reasons :

1. Natural cause :

a. At high temperature, sometimes dry grass catches fire which spreads throughout the forest.

b. Lightning.

2. Human cause :

a. Smoking

b. Camp fire

c. Recreation.

Q7. What do you understand by fuel efficiency?

Ans. The amount of heat energy produced on complete combustion of 1 Kg of fuel is known as Fuel efficiency.