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Combustion

1. If you hold a long copper wire in a candle flame, copper wire gets red hot in the non - luminous part whereas it just gets blackened in the luminous part. Why? 2. Goldsmiths often use a mettalic blow to direct non luminous part of flame on gold to give shape to gold ornaments. Why? 3. You observe circular greyish black ring formed on the glass slide in which there is no deposition in the middle of the ring. Why? 4. Water should not be used to extinguish fire caused by electric short circuit. Justify your statement. 5. Two paper cups, one filled with water and other empty, are heated over a bunsen burner. Empty cup catches fire immediately whereas the other does not. Why?
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Combustion

1. Gaseous fuels are considered the best.Write four poins in support of your answer. 2. What causes smog in winters? 3. If the amount of carbon dioxide increases in the atmosphere,what can be the effects of it? 4. What is global warming? Write it's one useful and one harmful effect of it. 5. What is acid rain? Write it's two harmful effects. 6. What is CNG?  Write three uses of CNG.
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Combustion

1. What is the colour of middle zone of flame? What happens in the middle zone of flame? 2. Which is the hottest part of the flame? What is the end product of combustion in this zone? 3. Write an experiment to show that wax vapours are present in innermost zone of candle flame. 4. When you put a glass slide over a candle flame grey ring is seen on the outer surface. Why? 5. A long copper wire put across a candle flame becomes red in non luminous part of the flame. Why? 6. What is calorific value of a fuel? Write it's unit also. 7. Write 4 characteristics of a good fuel.
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Combustion

1. Write two harmful effects of incomplete combustion. 2. What are the I'll effects of carbon monoxide gas? 3. What is a flame? 4. Draw a flame of a candle and label it. 5. Name the coolest part of the candle flame. What is it made up of? 6. What are inflammable substances? 7. How are human responsible for forest fires?
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Combustion

1. Differentiate between slow combustion and rapid combustion. 2. What is spontaneous combustion? 3. What is explosion? 4. What should be the action if the clothes of a person catch fire? 5. Water should not be used to extinguish fire caused by electric short circuit. Why? 6. How can we extinguish fire caused by oil or gas? 7. How does water and sand help in extinguishing fire?
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Combustion

1. What is ignition temperature? 2. A piece of paper is burnt with the help of a matchstick but wood is not. Why? 3. Explain how is it possible to boil water in a paper cup on a spirit lamp? 4. White phosphorus catches fire spontaneously during summer. Why? 5. Tip of a matchstick contains chemical that helps in catching fire but how does wood catch fire? 6. The flame of a burning candle goes off when we blow over it strongly.Give two reasons for it. 7. List three reasons necessary for sustaining combustion.
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Combustion

1. What are fuels? 2. Paper when burnt produces heat and light.What are these kinds of substances called? Give two other examples of it. 3. What is combustion? 4. What is fuel for our body? 5. Describe an experiment to show that air is necessary for combustion. 6. Why is oxygen called supporter of combustion? 7. A candle flame put in a jar covered with a cardboard is put off after sometime. Why?
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