Question 1: Explain
why some fibres are called synthetic.
Answer: There
are some fibres that are prepared by man by using chemicals. These are called
synthetic fibres. These are made of small units that join together to form long
chains. Examples of synthetic fibres are rayon, nylon, polyester, acrylic, etc.
Question 2: Mark
(tick) the correct answer.
Rayon is different from synthetic fibres because (a) it has
a silk-like appearance. (b) it is obtained from wood pulp. (c) its fibres can also
be woven like those of natural fibres.
Answer: Rayon is different from synthetic fibres because (a)
it has a silk-like appearance. (b) it is obtained from wood pulp. (tick) (c)
its fibres can also be woven like those of natural fibres.
Question 3: Fill
in the blanks with appropriate words.
(a) Synthetic fibres are also called _______ __ or _______
__ fibres.
(b) Synthetic fibres are synthesised from raw materials
called _______ __.
(c) Like synthetic fibres, plastic is also a _______ __.
Answer: (a) Synthetic fibres are also called __artificial__
or __man-made__ fibres.
(b) Synthetic fibres
are synthesised from raw materials called __petrochemicals__.
(c) Like synthetic
fibres, plastic is also a __polymer__.
Question 4: Give
examples which indicate that nylon fibres are very strong.
Answer: Nylon
fibres are very strong. It is used for making ropes used for climbing rocks and
for making parachutes. Their usage shows that nylon fibres have high tensile
strength.
Question 5: Explain
why plastic containers are favoured for storing food.
Answer: The
characteristics that make plastics favourable for storing food items are:
(i) Light weight
(ii) Lower price
(iii) Good strength
(iv) Easy handling
Question 6: Explain
the difference between thermoplastic and thermosetting plastics.
Answer: There
are two types of plastics: Thermosetting plastics and Thermoplastics
Thermosetting plastics and Thermoplastics.
|
Thermoplastic
|
Thermosetting plastic cannot be bent easily. It may break when forced
to bend.
|
Thermoplastic can be bent easily.
|
Thermosetting plastic cannot be softened by heating. Thus, it cannot
be reshaped once moulded.
|
Thermoplastic can be softened easily by heating. Thus, it can be
reshaped.
|
Question 7: Explain
why the following are made of thermosetting plastics.
(a) Saucepan handles (b) Electric plugs/switches/plug boards
Answer: (a)
Saucepan handles are made of thermosetting plastics because these plastics do
not get softened on heating. Also, thermosetting plastics such as bakelite are
poor conductors of heat.
(b) Thermosetting plastics such as bakelite are poor
conductors of heat and electricity. Therefore, they are used for making
electric plugs, switches, plug boards, etc.
Question 8: Categorize
the materials of the following products into ‘can be recycled’ and ‘cannot be
recycled’. Telephone instruments, plastic toys, cooker handles, carry bags,
ball point pens, plastic bowls, plastic covering on electrical wires, plastic
chairs, electrical switches.
Answer:
Cannot be
recycled
|
Can be
recycled
|
Telephone
instruments
|
Plastic toys
|
Cooker handles
|
Plastic chairs
|
Electrical
switches
|
Carry bags
|
Plastic
covering on electrical wires
|
|
Ball point
pens
|
|
Plastic bowls
|
Question 9: Rana
wants to buy shirts for summer. Should he buy cotton shirts or shirts made from
synthetic material? Advise Rana, giving your reason.
Answer: Rana
should buy shirts made from cotton. This is because cotton is a good absorber
of water. It can soak the sweat coming out of our body and expose it to the
environment. Thus, it helps in evaporating the liquid (sweat), thereby cooling
our body.
Question 10: Give
examples to show that plastics are non-corrosive in nature.
Answer: Plastics
are not corroded even if they come in contact with strong chemicals. This is
because of their non-reactive nature with most materials. For example, the
cleansing chemicals that we use at home are stored in plastic bottles, instead
of metal containers.
Question 11: Should
the handle and bristles of a tooth brush be made of the same material? Explain
your answer.
Answer: No.
The handle and bristles of a tooth brush should be made of different materials.
The handle of a toothbrush should be hard and strong, while the bristles should
be soft and flexible.
Question 12: ‘Avoid
plastics as far as possible’. Comment on this advice.
Answer: Plastics are non-biodegradable. Once introduced
into the environment, they take several years to decompose. Plastics add to the
environmental pollution. They cannot be burnt as when burnt, they release
poisonous gases. Plastic bags thrown in the garbage dump are swallowed by
animals like cows. These plastic bags choke their respiratory system and can
even prove fatal. Therefore, we should avoid plastics as far as possible.
Question 13: Match
the terms of column A correctly with the phrases given in column B.
A
|
B
|
(i) Polyester
|
a) Prepared by
using wood pulp
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(ii) Teflon
|
(b) Used for
making parachutes and stockings
|
(iii) Rayon
|
(c) Used to
make non-stick cookware
|
(iv) Nylon
|
(d) Fabrics do
not wrinkle easily
|
Answer:
A
|
B
|
(i) Polyester
|
a) Fabrics do
not wrinkle easily
|
(ii) Teflon
|
(b) Used to
make non-stick cookware
|
(iii) Rayon
|
(c) Prepared
by using wood pulp
|
(iv) Nylon
|
(d) Used for
making parachutes and stockings
|
Question 14: ‘Manufacturing
synthetic fibres is actually helping conservation of forests’. Comment. Answer:
Raw materials for natural fibres are mainly derived from plants and this
means cutting a lot of trees. This leads to deforestation. But raw materials of
synthetic materials are mainly petrochemicals. Hence, manufacturing synthetic
fibres helps in the conservation of forests.
Question 15: Describe
an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
We will design a circuit to see that thermoplastics are poor conductors
of electricity. We need a bulb, some wires, a battery, a piece of metal, and a
plastic pipe. Set up the circuit first with the metal and then with the plastic
pipe (as shown in the figure). After you switch on the current, you will
observe that the bulb glows in the former case. In the latter case, the bulb
does not glow. Hence, a plastic pipe (which is a thermoplastic) is shown to be
a poor conductor of electricity.
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