Questions with solution for Holly faith publication for class 8 Learnwell Science
Question: Why plastic should not be burnt?
Answer: Burning of plastic release toxic gases which causes air pollution that result various health hazard. This is why we should avoid burning plastic.
Question: Why does handle of cooking utensils are made up of Bakelite?
Answer: Bakelite is a kind of thermosetting plastic that do not get deform on heating at high temperature. This is why handle of cooking utensils are made up of Bakelite.
Question: Avoid wearing synthetic clothes while cooking. Give reason?
Answer: We should avoid wearing synthetic clothes while cooking because synthetic clothes catch fire easily and melt before burning.
Question: Give reason; Handle of heating pans are made up of plastics?
Answer: Handle of heating pans are made up of plastics because plastic being bad conductor of heat do not allow heat to pass into body.
Question: Electric wires are covered with plastics. Give reason?
Answer: Since plastics are poor conductor of electricity, do not allow current to pass through them. This is why electric wires are covered with plastics
Question: Why do electric plug not melt even the wire inside then get overheated?
Answer: Electrical plugs are made up of Bakelite that do not get deform on heating at high temperature.
Question: Why does rayon smell like burning paper; although it is a synthetic fibre?
Answer: Rayon smell like burning paper; although it is a synthetic fibre because rayon are obtain on mixing celuse a extract of wood pulp into chemicals.
Question: Why are plastic considered as environmental hazard?
Answer: Plastic considered as environmental hazard because of the following reason:
(i) Plastics do not decay in soil by natural process and cause soil pollution
(ii) Dumping of plastic into water cause threat to aquatic life.
(iii) Plastic bags thrown in to drain choke it out and support growth of disease causing pathogen like mosquito.
Question: Distinguish between Thermosetting plastics and Thermoplastic Plastic?
Thermosetting plastics are kind of plastic which once moulded cannot moulded again by heating.
Thermosetting plastics are kind of plastic whose polymers form highly cross linked chain on heating.
Bakellite , melanin, Formaldehyde are some of the examples of Thermosetting Plastic
Thermoplastic are kind of plastic which can be moulded again and again by heating and easily reused.
PVS, Polysterine , nylon , polythine are some of the examples of Thermoplastic Plastic
Polymers of thermoplastic Plastic have long chain without cross linked to each other.
Question: What is a synthetic fibre?
Answer: Fibres made by human beings using chemical substance is called synthetic fibre. A synthetic fibre is a chain of small unit of chemical substance joined together. These small units combine to form a large single unit called a polymer.
The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit. So, a polymer is made of many repeating units.
Question: List four measures to reduce the use of plastics and pollution caused by it?
(i) Do not throw plastic bags in the water bodies or on the road.
(ii) Take a cotton carry-bag or a jute bag while going for shopping.
(iii) Try to minimise the use of plastic materials e.g., use a steel lunch box instead of a plastic one.
(iv) Dispose plastic properly and store separately in bin at home.
Learnwell science class 8 chapter force and pressure and Friction Read
Blog Posts Categories
Join Us For Update
I am a school teacher and serving CBSE students community since 1995.