Q1: Why is ring of iron blade heated before fixing it into handle of a tool?
Ans: Ring of iron blade heated before fixing it into handle of a tool because on heating ring becomes slightly larger in size, therefore it expand and handle fits easily into it.
Q2: What happens when we keep on heating water in a pan?
Ans: When we keep on heating water in a pan, the quantity of water in the pan decreases.
Q3: Write two examples of changes which can be reversed.
a) Drying the wet clothes.
b) Liquid water into water vapour.
Q4: Why is the quantity of water in a pan decreases when we keeps on heating it?
Ans: The quantity of water in a pan decreases when we keeps on heating it because water changes into its vapour
Q5: Which of the following are reversible changes:
Ans: Melting of ice cream and changing shape of cloth by folding it.
Q6: Write two examples of changes which cannot be reversed?
a) Breaking a glass.
b) Preparing curd from milk.
Q7: Write True or false:
Q8: Conversion of water into water vapour is a reversible change. Why?
Ans: Conversion of water into water vapour is a reversible change because water vapour when cooled gets converted into liquid water again.
Q9: A blacksmith heats a piece of iron till it becomes red hot and then beats it into a desired shape. What changes have taken palace in iron on heating?
Ans: An iron expands and becomes soft on heating. Then it can be changed into desired shape.
Q10: On lightening the candle its length decreases. How can this be reversed?
Ans: If we take some wax in a pan and heat it, this change can be reversed.
Q11: Melting of ice is a reversible change. Why?
Ans: Melting of ice is a reversible change because on melting ice changes into water but the water can again be freezed to change it into ice
Q12: How can a change occur in a substance?
Ans: A change may occur by heating a substance or by mixing it with some other.
Q13: What changes occur in a match stick used for lightening? What type of change is it?
Ans: Match stick changes into ash and this is a change that cannot be reversed.
Q14: We dissolve salt in water. How can we reverse this change?
Ans: We can reverse this change by evaporation of water by which salt can be obtained. Water vapours are condensed to get liquid water.
Long Q & A:
Q1: How is metal rim fixed on a wooden wheel of a cart? How is the changes made in that metal?
Ans: Metal rim is made slightly smaller than the wooden wheel. On heating rim expands and fits into wheel. Cold water is then poured over rim, which contracts and fits tightly onto the wheel.
Q2: How the iron blade is fixed into a wooden handle in tools used to dig the soil?
Ans: Iron blade of tools has a ring in which the wooden handle is fixed. Normally the ring is slightly smaller in size than wooden handle. To fix handle ring is heated and it expands. Now handle easily fits into the ring. When ring cools down it contracts and fits into handle.