Class 8 Science Lesson 3 Inside Question

Class 8 Science Lesson 3 Inside Question and Answer NCERT & CBSE Board Here in this post. NCERT Class 8 Science Textbook Lesson 3 Inside Questions.

  • Grade: VIII
  • Lesson 3 Synthetic Fibres and Plastics.

Que.1) fill in the blanks.

(1) Synthetic fibers are also called—— or ——- fibers.

Ans- Rayon or artificial silk.

(2) A material which is not easily decomposed by natural process  it termed as —-

Ans- non- biodegradable.

(3) —— is another man-made fibre.

Ans- nylon

(4) ——- is an example of a plastic.


(5) Polythene and—- are examples of thermoplastics.

Ans- PVC

Que. 2) answers the following questions.

(1) What is polymer?

Ans- a synthetic chain of small units combine to form a large single unit called a Polymer. It is made of many repeating units.

(2) What are thermoplastic polymers?

Ans- A plastic which gets deformed easily on heating and can be bent easily are known as Thermoplastics.

(3) Define petrochemicals.

Ans- all the synthetic fibers are prepared by a number of processes using raw materials of petroleum origin called Petrochemicals.

(4) What are synthetic polymers or fibers?

Ans- the polymers or fibers made by humans beings is called synthetic fibers it is also known as man-made fibers.

(5) What are thermosetting polymers?

Ans- a plastic which moulded once can not be softened by heating these polymers called thermosetting polymers.

Que. 3) explain the following.

(1) What are synthetic fibers and types of synthetic fibers?

Ans-the synthetic fibers are made by human beings . they are also known as man-made fibers. Synthetic fibers is a chain of small units joined together. each small unit is a chemical substance. Many small units combine and forms a large single unit known as polymers.

There are many types of synthetic fibers for eg. Rayoon, Nylon ,Polyester and acrylic are some well known synthetic fibers.

(2) Give sort note on followings-

Rayon– fibers obtained by chemical treatment of wood pulp is called rayon or artificial silk. Although rayon s obtained from natural resources ,wood pulp, yet it is man made fibre. It is cheaper than silk and can be woven like silk fibers. It can be also dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.

Nylon– it is another man –made fiber. It is prepared from coal, water and air. It is the first fully synthetic fibre. It is strong ,elastic, and light. It is lustrous and easy to wash so it became very popular for making clothes. It is ued for making socks, ropes, tents, toothbrushes ,car seat etc.

Polyester- it is made from the fibre does not get wrinkled easily. It remains crips and is easy to wash, so it is quite suitable for making dress material. Terylene is a popular polyester. It is actually made up of the repeating units of a chemical called an ester. This fibrics are sold by names like polycot, polywool, terrycot etc. Polycot is a mixture of polyester and cotton.

Acrylic-  The  sweaters , shawls or blankets are prepared from synthetic fibers called Acrylic. The wool is obtained from acrylic is cheap. They are available in a variety of colours, they are more durable and affordable which makes them more popular than natural fibers.

(3) Give difference between thermosetting and thermoplastic polymers.


Thermoplastic polymers

Thermosetting polymers

A plastic which gets deformed easily on heating and can be bent easily are known as thermosetting polymers

A plastic which when moulded once can not be softened by heating these are called thermosetting plastics.

Polythene and PVC are examples  of thermoplastics.

These are used for manufacturing toyes, combs and various types of containers.

Bakelite and melamine are the examples of thermosetting plastics.

They are used for making electrical switches, handles of various utensils etc.

(4) Discuss characteristics properties of plastics.

Ans- the characteristics properties of plastic as following-

  • Plastic is non- reactive- plastic do not react with water and air. They are corroded easily. That is why they are used to store various kinds of materials, including many chemicals.
  • Plastic is light, strong and durable- plastic is very light, strong, durable and can be moulded into different shapes and sizes. It is used for various purposes plastic are generally cheaper than metals. They are widely used in the industry and for household articles.
  • Plastic are poor conductor- they are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screw divers are made of plastic.

This are the some characteristics properties of plastics.

Updated: December 19, 2020 — 1:45 am

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