Changes Around Us
Very Short Type Questions
(1) Ans: Heating or cooling.
(2) Ans: Cooling
(3) Ans: Reversible changes.
(4) Ans: Irreversible change.
(5) Ans: Irreversible.
(6) Ans: No.
(7) Ans: No.
(8) Ans: Yes.
(9) Ans: No.
(10) Ans: No.
(11) Ans: Melting max.
(12) Fill in the following blank with a suitable word:
When one or more properties of material become different, we say that a change has taken place in it.
Short Answer Type Questions
(13) Ans: (i) Formation of curd from milk,
(ii) Cooking of food,
(iii) Burning of fuels,
(iv) Drying of clothes, and
(v) Rusting of iron.
(14) Ans: Beneficial changes: The ripening of fruits.
Harmful changes: The spoiling of cooked food is harmful change.
(15) Ans: Melting of ice and Boiling of water.
(16) Ans: Burning of paper and burning of fuels.
(17) Ans: The iron blade of a soil digging tool is fixed to a wooden handle by the process of expansion on heating.
|Reversible Changes||Irreversible Changes|
|Melting of wax||Growth of a plant|
|Pulling of rubber string||Cooking food|
|Formation of curd from milk|
|Reversed||Can’t be reversed|
|Ironing of a cloth||Rusting of iron|
|Boiling of water to from steam||Ripening of fruits|
|Inflating a balloon|
(20) Ans: (a) Melting of wax: melting of wax is a reversible change.
(b) Burning of wax: the burning of wax is an irreversible change.
(21) Ans: The rolling of roti out of dough is a reversible change. And baking of roti is an irreversible change.
(22) Ans: (a) Inflating a balloon: inflating a balloon is a reversible change.
(b) Bursting an inflated balloon: the bursting of balloon is an irreversible change.
|Knitting of sweater||Boiling of an egg|
|Growth of nails||Making biogas from cow dung|
|Folding of paper|
|Reversed||Cannot be reversed|
|Drying of wet clothes||Grinding of grain to flour|
|Stretching a spring||Burning of incense stick|
|Melting of ice|
Long Answer Type Questions
(25) Ans: When one or more properties of a thing become different, we say that it has changed or a change has taken place in it.
- The melting of ice involves a change in state.
(26) Ans: Reversible changes: A change which can be reversed to form the original substance is called a reversible changes.
- Some of the examples are: Melting of ice, Boiling of water, Melting of wax etc.
Irreversible changes: A change which cannot be reversed to from the original substance is called an irreversible change.
- Some of examples are: Burning of paper, Burning of fuels, Growth of plant etc.
(27) Ans: The iron rim is made slightly smaller than the wooden wheel. The iron rim is heated uniformly by making a fire due to which it expands and becomes somewhat bigger in size. Being bigger in size, the hot iron rim is easily put around the wooden wheel. Cold water is then poured over the hot rim to cool it. On cooling the hot iron contracts and fits tightly on to the wooden wheel.
- The iron rims are fitted around wooden wheels by the process of expansion on heating.
(28) Ans: If we burn a piece of paper, it changes into ash and smoke. Now, we cannot combine the ash smoke to form the original piece of paper. So, the burning of paper is an irreversible change. But when we boil water by heating then it changes into steam. Now if we cool the steam then water is formed again. So, the boiling of water is a reversible change.
(29) Ans: Even the same material can undergo reversible change or irreversible change under different set of conditions.
- Examples: The folding of paper is reversible change. But the cutting of paper is an irreversible change.
- The rolling of roti out of dough is a reversible change. But baking of the roti is an irreversible change.
(30) Ans: That depends on the type of the material. if u have a volatile substance (like naphthalene balls), it can change its shape if it is in contact with air.
Multiple Choice Questions (MCQs)
(31) Ans: (a) water changing into ice
(32) Ans: (b) charcoal burns
(33) Ans: (c) state
(34) Ans: (c) ripening of fruit
(35) Ans: (c) B and C
(36) Ans: (b) boiling of an egg
(37) Ans: (d) C and D
(38) (a) Ironing of clothes
(39) Ans: (b) B and C
(40) Ans: (d) B and D