Physical Properties of Materials

1. Which one among the following metals is not a ferromagnetic material?

Which one among the following metals is not a ferromagnetic material?

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Cobalt
Silver
Iron
Nickel
This question was previously asked in
UPSC CISF-AC-EXE – 2024
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The correct answer is B) Silver.
Ferromagnetic materials are substances that are strongly attracted by a magnetic field and can be permanently magnetized. Common examples include Iron (Fe), Cobalt (Co), and Nickel (Ni). Silver (Ag) is a diamagnetic material, meaning it is weakly repelled by a magnetic field.
Materials can be classified based on their magnetic properties as diamagnetic, paramagnetic, or ferromagnetic. Diamagnetic materials have paired electrons and oppose external magnetic fields. Paramagnetic materials have unpaired electrons and are weakly attracted to magnetic fields. Ferromagnetic materials exhibit a strong attraction to magnetic fields due to the alignment of magnetic domains.

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2. What is the state of matter in a glowing fluorescent tube ?

What is the state of matter in a glowing fluorescent tube ?

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Gas
Liquid
Plasma
Bose-Einstein Condensate
This question was previously asked in
UPSC CISF-AC-EXE – 2022
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The correct answer is Plasma.
A fluorescent tube typically contains an inert gas (like argon) and a small amount of mercury vapour at low pressure. When an electric voltage is applied across the electrodes, it accelerates electrons within the tube. These electrons collide with the gas atoms and mercury atoms, causing them to become ionized (losing electrons) and excited. This creates a state of matter consisting of a collection of positively charged ions and negatively charged electrons, along with neutral atoms, that is overall electrically neutral. This state is known as plasma. The excited mercury atoms and ions emit ultraviolet (UV) light. The inside of the tube is coated with a phosphorescent material (phosphor) that absorbs the UV light and re-emits it as visible light, causing the tube to glow.
Plasma is often referred to as the fourth state of matter, distinct from solid, liquid, and gas. It is essentially an ionized gas. Plasma is the most abundant state of matter in the visible universe, found in stars, nebulae, lightning, auroras, and certain human-made applications like fluorescent lamps, neon signs, and plasma televisions.

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3. Bose-Einstein Condensate (BEC) is formed by cooling a gas of extremely

Bose-Einstein Condensate (BEC) is formed by cooling a gas of extremely low density, about one-hundredthousandth the density of normal air. This is treated as

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II state of matter
III state of matter
IV state of matter
V state of matter
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UPSC CISF-AC-EXE – 2017
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The common states of matter are Solid, Liquid, and Gas. Plasma is often considered the fourth state of matter, existing at very high temperatures where electrons are stripped from atoms. Bose-Einstein Condensate (BEC) is a distinct state of matter that occurs when a gas of bosons is cooled to temperatures very close to absolute zero. In a BEC, a large fraction of the bosons occupy the lowest quantum mechanical state, and macroscopic quantum phenomena become apparent. It is typically referred to as the fifth state of matter, following Solid, Liquid, Gas, and Plasma.
– The traditional states of matter are solid, liquid, and gas.
– Plasma is often considered the fourth state.
– Bose-Einstein Condensate (BEC) is a distinct state formed at extremely low temperatures and is considered the fifth state.
Bose-Einstein condensates were first experimentally realized in 1995 by Eric Cornell and Carl Wieman at the University of Colorado at Boulder, using a gas of rubidium atoms. They received the Nobel Prize in Physics in 2001 for this achievement, shared with Wolfgang Ketterle of MIT, who produced BECs in other atoms and demonstrated their properties. Fermionic condensates, a similar state for fermions, are sometimes referred to as the sixth state of matter.

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4. Consider the following statements : 1. Carbon fibres are used in the

Consider the following statements :

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  • 1. Carbon fibres are used in the manufacture of components used in automobiles and aircraftes.
  • 2. Carbon fibres once used cannot be recycled.

Which of the statements give above is/are correct?

1 only
2 only
Both 1 and 2
Neither 1 nor 2
This question was previously asked in
UPSC IAS – 2023
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The correct option is A, meaning only statement 1 is correct.
Statement 1 is correct. Carbon fibres and carbon fibre composites (CFRPs) are widely used in high-performance applications due to their high strength-to-weight ratio, stiffness, and corrosion resistance. They are integral in the manufacture of structural components for aircraft (e.g., wings, fuselage parts) and high-end automobiles (chassis, body panels), as well as sports equipment and wind turbine blades.
Statement 2 is incorrect. While challenging and less developed than traditional material recycling, carbon fibre composites *can* be recycled using various methods, including mechanical recycling (shredding/milling), pyrolysis (thermal decomposition), and solvolysis (chemical decomposition). Recycled carbon fibres can then be used in new composite materials. The infrastructure and economic viability are still developing, but it is not true that they *cannot* be recycled.
The recycling of carbon fibre composites is an active area of research and development aimed at reducing waste from manufacturing and end-of-life products and recovering valuable materials.

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5. Oil and water do NOT mix because of the property of

Oil and water do NOT mix because of the property of

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bulk modulus
shear strain
volume effect
surface tension
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UPSC CAPF – 2020
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Oil and water do not mix due to the property of surface tension (more specifically, interfacial tension between the two liquids).
Water is a polar molecule with strong hydrogen bonds, giving it high surface tension. Oil is nonpolar with weaker intermolecular forces. They have different cohesive forces and weak adhesive forces between them, causing them to minimize contact area. This tendency to minimize interfacial area is a manifestation of interfacial tension, which is related to the surface tensions of the individual liquids and their interactions.
Bulk modulus is a measure of resistance to uniform compression. Shear strain is a measure of deformation under shear stress. Volume effect is not a standard term in this context.

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6. Which one of the following is anisotropic in nature?

Which one of the following is anisotropic in nature?

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Glass
Rubber
Plastic
Quartz
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UPSC CAPF – 2018
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Quartz is a crystalline solid, and its physical properties (like refractive index, thermal conductivity, etc.) vary depending on the direction in which they are measured. This directional dependence of properties is known as anisotropy. Glasses, rubber, and most common plastics are amorphous solids (or largely amorphous), meaning their structure is disordered, and their properties are generally the same in all directions, making them isotropic.
Anisotropic materials have properties that vary with direction, typically due to their ordered internal structure (like crystals). Isotropic materials have properties that are the same in all directions, typically due to their disordered or randomly oriented structure (like amorphous solids or polycrystalline aggregates with randomly oriented grains).
Common examples of anisotropic materials include crystalline solids (like quartz, calcite, wood, and many metals in single crystal form). Isotropic materials include glass, amorphous polymers, liquids, and gases. Some materials can be made anisotropic through processing, like drawing plastic fibers or rolling metals, which introduces preferred orientation in the material’s structure.

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7. Liquid water is denser than ice due to

Liquid water is denser than ice due to

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higher surface tension
hydrogen bonding
van der Waals forces
covalent bonding
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UPSC CAPF – 2017
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Liquid water is denser than ice. This anomalous property is due to the unique structure formed by hydrogen bonding. In ice, water molecules form a rigid, open lattice structure (like a hexagonally ordered network) held together by hydrogen bonds. This structure is less compact than the arrangement of molecules in liquid water. In liquid water, while hydrogen bonds still exist, they are constantly breaking and reforming, allowing molecules to pack closer together, thus increasing the density compared to ice.
Hydrogen bonding in water is responsible for several of its anomalous properties, including the fact that solid water (ice) is less dense than liquid water.
Most substances contract and become denser when they solidify. Water expands and becomes less dense when it freezes. This property is crucial for life on Earth, as ice floats on water bodies, insulating the liquid water below and preventing lakes and rivers from freezing solid from the bottom up.

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8. The filament of electric bulb is generally made of tungsten because

The filament of electric bulb is generally made of tungsten because

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tungsten is cheap
durability of tungsten is high
light-emitting power of tungsten is high
melting point of tungsten is high
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UPSC CAPF – 2013
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The correct option is D. The filament of an electric bulb is generally made of tungsten because its melting point is high.
Incandescent light bulbs produce light by heating a wire filament to a very high temperature (around 2500-3000 °C) until it glows (incandescence). Tungsten has the highest melting point of all metals (3422 °C), allowing it to withstand these extreme temperatures without melting. This property is crucial for the filament’s operation.
While tungsten is durable and emits light, its high melting point is the primary reason for its use as a filament material. Other properties like its low vapor pressure at high temperatures also contribute to its suitability, reducing evaporation and prolonging filament life compared to materials with lower melting points. Tungsten is not particularly cheap compared to common metals.

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9. A thin pin of iron can be made to float on water (drinking) in a bowl.

A thin pin of iron can be made to float on water (drinking) in a bowl. This phenomenon is due to the

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surface tension of water
viscous nature of water
presence of ionic bonds in water molecules
presence of covalent bonds in water molecules
This question was previously asked in
UPSC CAPF – 2012
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A thin pin of iron, despite being denser than water, can float on the surface of water due to surface tension. Surface tension is the property of liquid surfaces that causes them to behave like a thin elastic membrane, resisting external force. The cohesive forces between water molecules create this tension.
– Surface tension is a property of liquids arising from cohesive forces between molecules.
– It allows the liquid surface to support small objects that are denser than the liquid, provided the object is placed gently and does not break the surface.
Viscosity is a measure of a fluid’s resistance to flow. Ionic and covalent bonds describe the chemical bonding within water molecules, not the macroscopic phenomenon of an object floating on the surface. The ability of insects like water striders to walk on water is also due to surface tension.

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10. Gases may be distinguished from other forms of matter by their :

Gases may be distinguished from other forms of matter by their :

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lack of colour.
ability to flow.
inability to form free surfaces.
ability to exert a buoyant force.
This question was previously asked in
UPSC CAPF – 2010
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Gases may be distinguished from other forms of matter by their inability to form free surfaces.
– Solids have fixed shape and volume. Liquids have fixed volume but take the shape of the container from the bottom up, forming a free surface under gravity. Gases take the shape and volume of the entire container.
– Gases expand to fill whatever container they are in, meaning they do not form a distinct boundary or “free surface” in the way liquids do.
– Lack of colour (A) is not universal for gases (e.g., NO2 is brown).
– Ability to flow (B) is characteristic of both liquids and gases (they are both fluids).
– Ability to exert a buoyant force (D) is also characteristic of both liquids and gases (both are fluids).
The defining characteristics of gases at a macroscopic level include: they have no fixed shape or volume, they are easily compressible, and they diffuse readily. The inability to form a free surface is a direct consequence of their molecules having high kinetic energy and weak intermolecular forces, causing them to spread out and occupy the entire volume of the container.

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