NCERT Textbook Exercise Questions (Important only)
Working with the Text
Q.1: What do you understand by the ‘flash point’ of a fuel?
Ans: Every fuel or combustible substance begins to burn only at a particular temperature. This temperature is called the ‘flash point’ or ‘kindling temperature’ of that substance.
(i) What are some common causes of fire?
(ii) In what sense is it a “bad master”?
Ans: (i) The common uses of fire are to cook food, warm our homes in winter, to generate electricity and so on.
(ii) If fire gets out of control, it can be dangerous. It can burn our houses, shops, vast forest areas and many more. It also kills and injures hundreds of people every year and causes destruction of huge properties.
Q.4: What are three main ways in which a fire can be controlled or put out?
Ans: The three main ways are as follows:
a. Take away one of the three things needed for burning.
b. Prevent oxygen (air) from reaching it.
c. Remove the heat to bring down the temperature below the flash point.
Q.6: Why does a burning candle go out when you blow on it?
Ans: When we blow on a burning candle, we remove the hot air around the flame. Thus, we bring down its temperature below its flash point and then the candle goes out.
Q.7: Spraying water is not good way of putting out an oil fire or an electrical fire. Why not?
Ans: Oil fire can not be put out by spraying water on it. The reason is that the oil floats to the top of water and continues to burn. Moreover water can flow quickly carrying the burning oil. Thus the fire spreads. Water should not be used on electrical fire. Since water is a good conductor of electricity so, the person spraying water can get electrocuted.
Q.8: What are some of the reasons you should do to prevent fire at home and in the school?
a) Keep the gas cylinder at a safe distance. Check its tube from time-to-time. The foul smell of the leaking gas should be tackled at the earliest.
b) The school and the office buildings generally catch fire because of short-circuit. So we should avoid overload and replace old wires. The meter should also be checked from time-to-time.
c) We must not keep inflammable or combustible things like kerosene, patrol or LPG gas etc carelessly.
d) Fire extinguishers should be installed in the high-rise buildings.
Working with Language
Q.2: Fill in the blanks in the sentences below with words in the box.
(i) Gandhiji’s life was devoted to the ——— of justice and fair play.
(ii) Have you insured your house against ———-?
(iii) Diamond is nothing but ———- in its pure form.
(iv) If you put too much coal on the fire at once you will —- it.
(v) Smoking is said to be the main —– of heart disease.
(vi) When asked by an ambitious writer whether he should put some —- into his stories, Sommerset Maugham murmured, “No, the other way round.”
(vii) She is a ——- copy of mother.
(viii) It is often difficult to ——– a yawn when you listen to a long speech on the value of time.
Ans: (i)cause (ii)fire (iii)carbon (iv)smother (v)cause (vi)fire (vii)carbon (viii)smother
Q.4: Use the words given in the box to fill in the blanks in the sentence below.
(i) The cat chased the mouse —- the lawn.
(ii) We were not allowed to cross the frontier. So we drove ——- it as far we could and came back happy.
(iii) The horse went ——- the winning post and had to be stopped with difficulty.
(iv) It is not difficult to see ——– your plan. Any one can see your motive.
(v) Go —— the yellow line, then turn left. You will reach the post office in five minutes.
Ans: (i) across (ii) along (iii) past (iv) through (v) along
Q.1: Fire is a good servant but a bad master. Explain.
Ans: Fire can be is a very useful thing as long as it is kept under control. It has a number of uses. We cook our food, warm our homes during winter, produce electricity with the help of fire. But it becomes deadly when it goes out of control. Then it can burn our houses, shops, offices, schools and thus causes huge loss of our properties. It can even kill and injure men and animals.