Synthetic Fibres and Plastics – Short Answer Type Questions
Class 8
Science
Chapter 3
Synthetic Fibres and Plastics — 50 Short Answer Questions (Topic-wise)
CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT
Content Bank — Chapter highlights
- Definitions and differences: natural vs synthetic fibres
- Major synthetic fibres: rayon, nylon, polyester, acrylic
- Plastics: thermoplastics vs thermosetting plastics
- Properties, uses, care, environmental concerns and recycling
CBSE Board Examinations — Chapter Presentation (Systematic):
- Question Style: Short Answer Type (3–6 lines) aimed at conceptual clarity and exam readiness.
- Use these topic-wise Q&A for classroom tests, homework and revision before exams.
Topic 1: Basics & Definitions (Q1–Q8)
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Q1: What is a fibre? Give one example.
A1: A fibre is a long, thin thread-like structure used for making textiles. Example: cotton, a natural fibre used widely in clothing.
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Q2: Define synthetic fibre.
A2: A synthetic fibre is a man-made fibre produced through chemical processes, often from petrochemicals or regenerated natural polymers, designed to have specific properties not always found in natural fibres.
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Q3: What is a polymer?
A3: A polymer is a large molecule composed of repeating units called monomers joined together; both synthetic fibres and plastics are made of polymers.
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Q4: Mention two reasons synthetic fibres were developed.
A4: To provide materials with greater strength, elasticity, wrinkle-resistance and lower maintenance than some natural fibres, and to meet growing demand for textiles not available from natural sources.
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Q5: Give two examples of natural fibres.
A5: Cotton (plant-based) and wool (animal-based) are common natural fibres used in clothing and textiles.
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Q6: What is the main difference between fibre and fabric?
A6: A fibre is a single thread-like unit; a fabric is a material made by weaving, knitting or bonding many fibres together to form a cloth.
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Q7: Define plastic in simple terms.
A7: Plastic is a synthetic material made of polymers that can be moulded into desired shapes when heated and solidified on cooling.
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Q8: Why is it important to study synthetic fibres and plastics?
A8: Because they are widely used in everyday life, understanding their properties, uses and environmental impact helps in making informed choices and handling them responsibly.
Topic 2: Important Synthetic Fibres (Q9–Q18)
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Q9: What is rayon and how is it produced?
A9: Rayon (viscose) is a regenerated cellulose fibre produced from wood pulp; the cellulose is chemically treated and reformed into fibres that resemble natural silk or cotton.
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Q10: State one characteristic and one use of rayon.
A10: Characteristic: comfortable and absorbent like cotton. Use: dress materials and linings due to its silk-like feel.
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Q11: What is nylon? Mention two of its properties.
A11: Nylon is a fully synthetic polyamide fibre known for its high strength and elasticity; it is also abrasion-resistant and quick-drying.
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Q12: Give two common uses of nylon.
A12: Nylon is used for making stockings, ropes, parachutes and sometimes blended with other fibres for durable fabrics.
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Q13: What are polyester fibres and why are they popular?
A13: Polyester is a synthetic polymer fibre appreciated for its strength, resistance to shrinking, quick-drying property and ease of care, making it popular for clothing and home textiles.
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Q14: Mention one advantage of acrylic fibres.
A14: Acrylic fibres are lightweight, warm and have a wool-like feel, making them suitable as wool substitutes in sweaters and blankets.
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Q15: Which synthetic fibre is commonly used in polyester-cotton blends?
A15: Polyester is commonly blended with cotton (poly-cotton) to improve durability and reduce wrinkling while retaining comfort.
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Q16: Why are some synthetic fibres called semi-synthetic?
A16: Semi-synthetic fibres like rayon are made from natural polymers (cellulose) that are chemically processed and regenerated into fibres, so they are partly natural and partly synthetic.
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Q17: How does the strength of nylon compare to cotton?
A17: Nylon is generally stronger and more elastic than cotton, making it suitable for applications needing high tensile strength.
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Q18: Name one fibre suitable for making warm clothing and why.
A18: Acrylic is suitable because it is wool-like and retains warmth while being lighter and resistant to moth damage.
Topic 3: Properties and Uses (Q19–Q30)
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Q19: Why is polyester often used for outdoor clothing?
A19: Polyester resists water absorption, dries quickly and resists stretching and shrinking, making it suitable for outdoor apparel.
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Q20: Explain why rayon is not as strong when wet.
A20: Rayon is made of regenerated cellulose which swells and weakens when wet, reducing its tensile strength compared to dry conditions.
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Q21: How does elasticity affect fabric performance?
A21: Elastic fabrics (like nylon blends) stretch and return to shape, improving comfort and fit, especially in sportswear and hosiery.
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Q22: Give one example of an industrial use of synthetic fibres.
A22: Synthetic fibres like nylon and polyester are used in seat belts, conveyor belts and ropes due to their strength and durability.
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Q23: Which property of a fibre determines how quickly it dries?
A23: The hydrophilicity or water-absorption capacity determines drying speed; fibres that absorb less water (e.g., polyester) dry faster.
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Q24: Why are synthetic fibres often blended with cotton?
A24: Blending combines cotton's comfort and absorbency with synthetic fibres' durability and wrinkle-resistance, creating balanced fabrics for everyday use.
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Q25: How does fibre structure influence warmth?
A25: Fibres that trap air within their structure (e.g., wool-like acrylic) provide insulation and retain body heat, increasing warmth.
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Q26: What makes a fibre suitable for medical sutures?
A26: Biocompatibility, strength, controlled absorbability and minimal tissue reaction make certain synthetic fibres suitable for sutures.
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Q27: Why is colourfastness important in textiles?
A27: Colourfastness ensures dyes remain stable during washing and exposure, maintaining appearance and reducing fading.
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Q28: Name one fabric care tip to extend the life of synthetic clothes.
A28: Wash on gentle cycles with suitable detergents, avoid high-temperature drying and follow label instructions to prevent damage.
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Q29: How do manufacturers add flame resistance to some plastics?
A29: By incorporating flame-retardant additives or using inherently heat-resistant polymers (thermosetting resins) during manufacture.
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Q30: What is a common test to check fibre absorbency?
A30: Place a drop of water on the fabric and observe whether it is absorbed quickly (absorbent) or beads up (non-absorbent).
Topic 4: Plastics — Types & Uses (Q31–Q38)
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Q31: Distinguish between thermoplastics and thermosetting plastics.
A31: Thermoplastics soften on heating and can be remoulded multiple times (e.g., polyethylene), while thermosetting plastics harden irreversibly after heating and cannot be remoulded (e.g., bakelite).
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Q32: Give two examples of thermoplastics and their uses.
A32: Polyethylene (PE) used in plastic bags and containers; PVC used in pipes and window frames for its durability and chemical resistance.
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Q33: Name two thermosetting plastics and one use each.
A33: Bakelite — electrical switches and handles (heat-resistant); Melamine — kitchenware and laminates (hard and scratch-resistant).
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Q34: Why are plastics widely used for packaging?
A34: Plastics are lightweight, moisture-resistant, mouldable and relatively inexpensive, making them ideal for protecting and transporting goods.
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Q35: What properties make PVC suitable for pipes?
A35: PVC is chemically resistant, durable, rigid and easy to mould, making it suitable for water and drainage pipes.
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Q36: Explain why bakelite is a good electrical insulator.
A36: Bakelite is a thermosetting resin that is heat-resistant and does not conduct electricity, providing safe insulation for electrical components.
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Q37: What is PET and where is it commonly used?
A37: PET (polyethylene terephthalate) is a strong, lightweight thermoplastic commonly used for beverage bottles and food containers because it is safe and recyclable.
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Q38: How does polymer structure affect plastic properties?
A38: The length, branching and cross-linking of polymer chains determine flexibility, melting point and strength; more cross-linking usually increases rigidity and heat resistance.
Topic 5: Environmental Concerns & Recycling (Q39–Q46)
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Q39: Why are many plastics considered pollutants?
A39: Because most conventional plastics are non-biodegradable, they persist in the environment, clog landfills and harm wildlife when mismanaged.
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Q40: What are microplastics and why are they a concern?
A40: Microplastics are tiny plastic particles released from larger plastics or synthetic fibres during washing; they enter waterways and the food chain, posing ecological and health risks.
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Q41: Explain the 3R principle briefly.
A41: Reduce (minimise use of disposable items), Reuse (use items multiple times) and Recycle (process waste into new materials) to lower environmental impact.
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Q42: Name one method used to recycle thermoplastics.
A42: Mechanical recycling: collection, sorting, melting and remoulding thermoplastics into new products.
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Q43: Why should burning plastics be avoided?
A43: Burning plastics releases toxic gases like dioxins and furans that are hazardous to human health and the environment.
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Q44: How can households reduce plastic waste?
A44: By using cloth bags, avoiding single-use plastics, segregating waste for recycling and choosing reusable containers.
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Q45: What should you look for on a plastic item to know its recyclability?
A45: Look for the recycling symbol and a number/code (plastic identification code) that indicates the type of plastic and recycling options.
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Q46: Suggest one school activity to raise awareness about plastic pollution.
A46: Organise a plastic-free day and a campus clean-up followed by a session on recycling and alternatives to single-use plastics.
Topic 6: Care of Fabrics, Practicals & Revision (Q47–Q50)
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Q47: How should synthetic garments be cared for to prolong life?
A47: Follow label instructions, wash gently on recommended cycles, avoid high heat drying or ironing and store away from direct sunlight to reduce degradation.
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Q48: Describe a safe classroom demonstration to compare burning behaviour of cotton and a synthetic fibre.
A48: Under teacher supervision and safety measures, burn tiny samples: cotton tends to burn to ash and smell like paper, while many synthetics melt and produce a sharp plastic-like odour; emphasise safety and ventilation.
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Q49: Give one quick revision tip for this chapter.
A49: Make comparison tables (fibre/plastic — properties — uses — care) and memorise key examples for quick recall during exams.
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Q50: What is the exam-style answer structure for a 3-mark question on this chapter?
A50: Begin with a clear definition (1 line), give two or three key points or examples (2–3 lines) and conclude with a short sentence linking property to use.
Note: These Short Answer Questions with Answers are organised topic-wise and strictly follow the NCERT syllabus, making them ideal for CBSE Class 8 board exams standard.