Chapter No. 5

Polymers have low density because they are made up of long chains of repeating molecular units. These chains are loosely packed together, resulting in a material with low density. Additionally, polymers often contain lightweight elements such as carbon and hydrogen, further contributing to their low density.

Piezoelectric materials experience a change in shape when an electric field is applied to them. This phenomenon is known as the piezoelectric effect. When an electric field is applied, the material undergoes a displacement or deformation, which can be used in various applications such as sensors, actuators, and transducers. This property makes piezoelectric materials useful in a wide range of fields including electronics, medical devices, and energy harvesting.

Nano materials are used for water purification in desalination by reverse osmosis. Reverse osmosis is a process that removes salt and other impurities from seawater to make it suitable for drinking. Nano materials, such as nanotubes and nanofibers, have unique properties that make them effective in water purification processes. They have a large surface area, which allows for more efficient adsorption and filtration of contaminants. Additionally, their small size allows them to easily pass through membranes, increasing the overall efficiency of the desalination process.

Quartz is considered a smart material because it exhibits piezoelectric properties, meaning it can generate an electric charge when mechanical stress is applied to it. This property allows quartz to be used in various applications such as sensors, actuators, and oscillators.

Both the bottom-up and top-down approaches are methods for the synthesis of nanoparticles. The bottom-up approach involves building nanoparticles from smaller components or atoms, gradually assembling them into larger structures. On the other hand, the top-down approach involves breaking down larger materials into nanoparticles through techniques such as grinding, milling, or lithography. Therefore, both A (bottom-up approach) and B (top-down approach) are valid methods for synthesizing nanoparticles.

Rubber is a linear polymer because it consists of long chains of repeating monomer units that are connected in a straight line. This linear structure gives rubber its unique properties such as elasticity and flexibility.

Nano-particles are extremely small particles with sizes ranging from 0.1nm to 100nm. This range is considered to be the size range for nano-particles. Therefore, option A, 0.1nm-100nm, is the correct answer.

PVC is classified as a thermoplastic material because it can be melted and re-melted multiple times without undergoing any significant chemical change. Thermoplastics have a linear or branched structure, and they soften when heated and harden when cooled. This property allows PVC to be easily molded into various shapes and forms, making it a versatile material for many applications. On the other hand, thermosetting materials undergo a chemical change when heated and cannot be melted or reshaped once they have been set.

As the size of a particle decreases, the ratio of surface area to volume increases. This means that there is a larger surface area available for interactions with the surroundings. In the case of nano materials, this increased surface area leads to more atoms or molecules being present at the surface, which results in weaker intermolecular forces. Consequently, the particles require less energy to break these weak intermolecular forces and transition from a solid to a liquid state, resulting in a lower melting point. Therefore, the statement that the melting point of nano materials decreases with a decrease in size of the particle is true.

Reinforced concrete is used in columns and beams for construction because it combines the strength and durability of concrete with the added reinforcement of steel bars or mesh. This combination allows the concrete to withstand higher loads and resist cracking and bending, making it suitable for supporting heavy structures. Reinforced concrete is commonly used in construction due to its versatility, cost-effectiveness, and ability to be molded into various shapes and sizes.

Polymethyl methacrylate (PMMA) is used in contact lenses.

Neoprene is a type of synthetic rubber that has various applications. It is known for its resistance to oil, heat, and weathering, making it suitable for different purposes. A hose cover made of neoprene can provide protection and insulation for hoses, while neoprene footwear can offer durability and waterproofing. Neoprene is also commonly used in brake diaphragms due to its ability to withstand high temperatures and resist chemical degradation. Therefore, all of the given options (A, B, and C) are correct applications of neoprene.

Photochromic material is used in sunglasses. This type of material has the ability to darken when exposed to UV light and lighten when the UV light is removed. This allows the sunglasses to automatically adjust to different lighting conditions, providing the wearer with optimal visibility and protection from the sun's harmful rays.

Thermosetting plastics are materials that undergo a chemical change when heated and molded under pressure. This chemical change causes the plastic to cross-link and form a rigid and permanently hard product. Unlike thermoplastics, which can be melted and reshaped multiple times, thermosetting plastics cannot be remolded once they have undergone this chemical change. Therefore, option A correctly describes the characteristic of thermosetting plastics.

Perspex is a trade name for Poly methyl methacrylate, commonly known as acrylic. Acrylic is a transparent thermoplastic that is often used as a lightweight and shatter-resistant alternative to glass. It is commonly used in applications such as windows, signs, displays, and lighting fixtures.

Thermosetting plastics have the property of a little shrinkage, meaning they do not shrink significantly when cooled. They are also transparent, allowing light to pass through. Additionally, they have good insulating properties, meaning they are able to prevent the flow of heat or electricity. Therefore, the correct answer is D, all of the above.

The correct answer is A) one third. This means that the resilience of NBR is one third of the resilience of natural rubber.

PMMA, or polymethyl methacrylate, is a type of plastic that is manufactured through addition polymerization of methyl methacrylate. It is commonly known as acrylic or acrylic glass and is used in various applications such as windows, lenses, and signage. PMMA is known for its transparency, durability, and weather resistance, making it a popular choice in many industries.

Magneto restrictive materials convert magnetic energy into kinetic energy.

Thermoplastic plastics should not be heated above their decomposition temperature because they will break down and lose their structural integrity. Unlike thermosetting plastics, which can withstand high temperatures without decomposing, thermoplastic plastics can melt and become deformed when exposed to excessive heat. Therefore, it is important to carefully control the temperature when working with thermoplastic plastics to avoid damaging or destroying the material.

Elastomers are known for their high ductility, meaning they can be stretched and deformed significantly without breaking. They are also bad conductors of heat, meaning they do not easily transfer heat. Additionally, elastomers have high resistance to abrasion, making them durable and suitable for applications where wear and tear is a concern. Therefore, all of the given options (A, B, and C) are properties of elastomers.

Nylons have poor resistance to hot water, alcohol, and ultraviolet light. This means that they are not able to withstand exposure to these elements without experiencing damage or degradation.

Magnetostrictive materials are affected by magnetic fields. When a magnetic field is applied to these materials, they undergo a change in shape or dimensions. This phenomenon is known as the magnetostrictive effect. Therefore, the correct answer is B, magnetic field.

The density of glass wool is a measure of how much mass is contained within a given volume. A lower density indicates that there is less mass packed into the same volume, while a higher density indicates more mass packed into the same volume. Therefore, a density of 24 kg/m3 means that there is less mass in each cubic meter of glass wool compared to the other options provided.

Glasswool is a type of insulation material that can be used in both heat and cold insulation. It is made from recycled glass and has excellent thermal insulation properties. It is able to trap air pockets within its structure, which helps to reduce heat transfer through conduction. This makes it effective in both hot and cold environments, making it a versatile choice for insulation applications.

Piezoelectric materials produce voltage when stress is applied. This is because these materials have the ability to convert mechanical energy (stress) into electrical energy (voltage) due to their unique crystal structure. When stress is applied to a piezoelectric material, it causes a displacement of positive and negative charges within the material, resulting in the generation of an electric potential difference or voltage across the material. This property of piezoelectric materials is widely used in various applications such as sensors, actuators, and transducers.

Thermosetting plastics have a three-dimensional molecular structure. Unlike thermoplastic plastics, which can be melted and reshaped multiple times, thermosetting plastics undergo a chemical reaction during the curing process that permanently sets their shape. This chemical reaction creates strong cross-linking bonds between the polymer chains, resulting in a rigid and infusible material. Therefore, the correct answer is B thermosetting plastic.

Acidity affects pH sensitive material because pH is a measure of the concentration of hydrogen ions in a solution. Acidity is determined by the concentration of hydrogen ions, so an increase in acidity will result in an increase in the concentration of hydrogen ions, leading to a decrease in pH. Therefore, pH sensitive materials will respond to changes in acidity by changing their pH value.

Shape memory materials are also known as thermo responsive materials because they can change their shape in response to changes in temperature. These materials have the ability to "remember" their original shape and return to it when heated. This property makes them useful in various applications such as medical devices, aerospace engineering, and textiles.

Gold nanoparticles absorb 100% of light and do not shine because of a phenomenon called surface plasmon resonance. When light interacts with gold nanoparticles, the electrons in the metal oscillate collectively, absorbing the light energy and converting it into heat. This absorption of light prevents the gold nanoparticles from reflecting or scattering light, resulting in their lack of shine. Zinc sulphide, titanium carbide, and cadmium sulphide do not have the same properties and therefore do not absorb 100% of light.

Glasswool is a type of insulation material that is commonly used in aeroplanes for both thermal and sound insulation. It is made from fine glass fibers that are woven together to form a dense mat. The structure of glasswool traps air pockets, which helps to prevent the transfer of heat and sound. It is lightweight, flexible, and has excellent thermal and acoustic properties, making it an ideal choice for insulation in aeroplanes.

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The correct answer is B three dimensional cross linked. This means that the polymer chair has a three-dimensional network of cross-linked bonds, which gives it stability and strength. This type of structure is commonly found in polymers that are designed to be rigid and durable.

Polyethylene terephthalate (PET) is commonly used in various applications due to its properties such as strength, durability, and resistance to chemicals. It is commonly used in the production of bottles, packaging materials, and textiles. However, it is not typically used in electrical connections. This is because PET is not a good conductor of electricity and may not provide the necessary conductivity and safety required for electrical connections. Therefore, it is not commonly used in this application.

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After the removal of external force, smart materials completely regain their original properties. This means that they are able to return to their original shape, size, and characteristics without any permanent deformation or damage. Unlike other materials that may experience permanent changes or damage after being subjected to external forces, smart materials have the ability to recover and restore themselves to their original state.

Ceramics are commonly used in sanitary wares. They are durable, non-porous, and resistant to stains, making them ideal for use in bathroom fixtures such as sinks, toilets, and bathtubs. Ceramics also have a smooth surface, which makes them easy to clean and maintain. Additionally, ceramics can withstand high temperatures and are not easily damaged by chemicals or moisture, further enhancing their suitability for use in sanitary wares.

Thermoplastic materials are able to be formed into a specific shape when pressure is applied, and once they cool down, they retain that shape permanently. This is in contrast to thermosetting materials, which undergo a chemical change when heated and cannot be reshaped once they have solidified. Therefore, option A accurately describes the characteristics of thermoplastic materials.

Acrylic is a type of thermoplastic material that is commonly used in various applications. It is a lightweight and durable material that can be easily molded and shaped when heated. It has good transparency and weather resistance, making it suitable for use in products such as windows, lenses, and outdoor signs. Acrylic is also known for its high impact strength and resistance to chemicals, making it a popular choice for items such as aquariums and protective barriers. Therefore, option A, acrylic, is the correct answer as it is a thermoplastic material.

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Phenol formaldehyde is a type of plastic that is known to discolor on aging when exposed to sunlight. This is because the UV radiation in sunlight can cause the chemical structure of the plastic to break down, leading to a change in color. This is a common phenomenon observed in many types of plastics, and it is important to consider this when using or selecting materials for outdoor applications.

Shape memory materials are used in civil structures. These materials have the ability to "remember" their original shape and return to it after being deformed. This property makes them ideal for applications in civil engineering, such as in bridges and buildings, where they can be used to absorb and recover from structural deformations caused by external forces or environmental conditions. Shape memory materials can enhance the safety and durability of civil structures by providing them with the ability to self-repair and adapt to changing conditions.

Nano technology is the process used for making high power magnets. This technology involves manipulating and controlling materials at the nanoscale level, which allows for the creation of magnets with enhanced properties such as higher magnetic strength and improved performance. Powder metallurgy and polymerization are not specifically used for making high power magnets, and the option "none of these" is incorrect as nano technology is indeed the correct answer.

Glasses are used in the windscreen of motors.

Nylons are commonly used in applications such as clothing, gears, and ropes due to their high strength and durability. However, they are not typically used in refrigerator gaskets, which are usually made from materials that provide a better seal and insulation.

Quartz is classified as a piezoelectric material. Piezoelectric materials are those that can generate an electric charge when mechanical stress is applied to them. Quartz, in particular, has a unique crystalline structure that allows it to generate an electric charge when pressure or mechanical stress is applied to it. This property makes quartz widely used in various applications such as electronic devices, sensors, and oscillators.

Thermosetting plastics are chemically inert to organic solvents. This means that they do not react or dissolve when exposed to organic solvents. Unlike thermoplastic plastics, which can melt and be reshaped when heated, thermosetting plastics undergo a chemical reaction when heated and become permanently set. This chemical reaction creates a cross-linked network structure that makes them resistant to solvents. Therefore, thermosetting plastics are the correct answer as they do not react with or dissolve in organic solvents.

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Alcad is a type of laminated composite material. Laminated composites are made by layering multiple materials together, typically alternating between layers of reinforcement and matrix materials. Alcad is a specific type of laminated composite that is made by bonding layers of aluminum and copper together. This material is commonly used in electrical applications due to its high electrical conductivity and low electrical resistance. Therefore, option A, alcad, is the correct answer as it is a laminated composite material.

Rolling is not used for manufacturing ceramics because it is a process primarily used for shaping metals. Ceramics are typically formed through methods such as injection molding, sintering, and hot processing, which involve the use of heat and pressure to shape and solidify ceramic materials. Rolling, on the other hand, involves passing a metal material between two rollers to reduce its thickness or change its shape. Therefore, rolling is not a suitable method for manufacturing ceramics.