class 8 assignment combustion flame and fuel

COMBUSTION,FLAME AND FUEL.

CLASS 8

ASSIGNMENT

1. A substance which reacts with oxygen giving heat is called a combustible substance. Which, one of the following is a combustible substance?
 (a) iron nail (c) stone piece (b) glass (d) wood 
2. Which one of the following has the highest calorific value?
 (a) kerosene (c) LPG (b) biogas (d) petrol 
3. Magnesium ribbon on burning in air produces
 (a) magnesium oxide, water and light
 (b) magnesium oxide and heat
 (c) magnesium oxide, heat and light 
(d) magnesium oxide, water and heat 
4. Which of the following is not a combustible substance?
 (a) camphor (c) straw (b) glass (d) alcohol 
5. The substance that does not burn with flame is
 (a) LPG (c) dry grass (b) camphor (d) charcoal
 6. On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of nonavailability of (a) oxygen (c) carbon dioxide (b) water vapours (d) wax
 7. If a person’s clothes catches fire, the best way to extinguish the fire is to: 
(a) throw water on the clothes. (b) use fire extinguisher. 
(c) cover the person with a woolen blanket. 
(d) cover the person with a polythene sheet. 
 8. The substance expected to have the highest ignition temperature out of the following is
 (a) kerosene (c) coal (b) petrol (d) alcohol 
9. Choose the correct statement about inflammable substances from the following. They have: 
(a) low ignition temperature and cannot catch fire easily.
 (b) high ignition temperature and can catch fire easily. 
(c) low ignition temperature and can catch fire easily. 
(d) high ignition temperature and cannot catch fire easily. 
10. Choose the incorrect statement from the following. Forest fires are usually due to:
 (a) carelessness of humans (b) cutting of trees 
(c) heat of sun (d) lightning strike
 11. The calorific value of a fuel is expressed in a unit called 
(a) kilojoule per litre 
(b) kilojoule per gram 
(c) kilogram per mililitre
 (d) kilojoule per kilogram 
12. In villages, people use wood as fuel because: 
(a) it is considered to be an ideal fuel.
 (b) of its easy availability and low cost.
 (c) it is environment friendly.
 (d) it catches fire easily. 
13. Which among the following is considered as the cleanest fuel? (a) cow dung cake (c) kerosene (b) petrol (d) hydrogen gas 
14. Choose the incorrect statement from the following. A good fuel is one which:
 (a) is readily available.
 (b) produces a large amount of heat.
 (c) leaves behind many undesirable substances. 
(d) burns easily in air at a moderate rate. 
15. Shyam was cooking potato curry on a chulha. To his surprise he observed that the copper vessel was getting blackened from outside. It may be due to: 
(a) proper combustion of fuel.
 (b) improper cooking of potato curry.
 (c) improper combustion of the fuel.
 (d) burning of copper vessel. 
 VERY SHORT ANSWER QUESTIONS 
16. Fill in the blanks in the following sentences.
 (a) A ____________ process in which a substance reacts with __________ to give off heat is called combustion. 
(b) When the clothes of a person catch __________, the person is covered with a __________ to extinguish fire. 
(c) The __________ temperature at which a substance catches fire is called its __________ temperature. 
(d) The substances which have very ________________ ignition temperature and can easily catch fire with a flame are called __________ substances.
 (e) The substances which vapourise during __________, give flame. 
17. Some words (underlined) in the following sentences are jumbled up. Write them in their correct form. 
(a) Seldie is a combustible substance.
 (b) Slags is a non-combustible material. 
(c) Chittsmack does not burn by itself. 
(d) Some substances on combustion produce thea and mafel.
 (e) The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its ficalroic value.
 18. Two glass jars A and B are filled with carbon dioxide and oxygen gases, respectively. In each jar a lighted candle is placed simultaneously. In which jar will the candle remain lighted for a longer time and why?
 19. Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity. 
20. Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Gas (CNG) in big cities?