Classification of Materials MCQ Quiz in मराठी - Objective Question with Answer for Classification of Materials - मोफत PDF डाउनलोड करा

The correct answer is fluoro carbon.

Key Points

• Teflon
  • ​Teflon is a fluorocarbon.
  • It is also called polytetrafluoroethylene.
  • Teflon is a synthetic material used to cover the surface of an object and transmit nonstick properties.
  • It is very non-reactive hence it is used as a non-stick coating.
  • It is a solid polymer.
• Properties of Teflon
  • ​It is a white solid compound at room temperature.
  • The melting point of Teflon is 600K.
  • It exhibits good resistance to heat and low temperatures.
  • It has less water absorbing capacity.
• Uses of Teflon
  • It is used to make waterproof clothing.
  • It is used in making non-stick cookware.
  • It is used for coating medical instruments (surgical instruments).
  • Due to its high resistance to corrosion, it is used for coating the lining of laboratory equipment.

Explanation:

Various alloys of copper are brass, bronze, bell metal, gunmetal, aluminium bronze and German silver.

Bronze: Bronze is an alloy of copper and tin and carries better mechanical properties and corrosion resistance as compared to brass.

Brass: It is an alloy of copper and zinc which is highly resistant to corrosion.

Muntz Metal: Muntz metal (yellow metal) is also a type of brass which contains 40% zinc with excellent tensile strength and lesser ductility.

Gun Metal: It is an alloy of copper, tin and zinc. Gun metal is used for bearings, steam pipe fittings, valves and gears.

German Silver: It is nickel, zinc, and copper alloy with 25%, 15% and 60% composition, respectively. It is highly corrosive in nature.

Explanation:

Pig iron:

• Pig iron is obtained by the chemical reduction of iron ore. This process of reduction of the iron ore to pig iron is known as smelting.
• The main raw materials required for producing pig-iron are: Iron ore, coke, limestone
• Pig iron is the intermediate product of smelting iron ore.
• In a blast furnace, coke (C) reacts with oxygen to form carbon monoxide, which then reacts with iron oxide to form carbon dioxide and pig iron.
• A blast furnace is a type of furnace which converts a mixture of metallic ore, coke, and flux into liquid metal by introducing air under high pressure.
• Iron oxide must be reduced in order to obtain iron and this can be done only in a blast furnace.
• Pig iron has a very high carbon content, typically 3.5 - 4.5%.

Superconductor:

A superconductor is a material that achieves superconductivity, which is a state of matter that has no electrical resistance and does not allow magnetic fields to penetrate.

Properties of an ideal superconductor:

1.)  Critical temperature / Transition temperature:

• The temperature below which the material changes from conductors to superconductors is called critical temperature or transition temperature.
• The transition from conductors to superconductors is sudden and complete.

2.) Zero Electric Resistance/Infinite Conductivity:

• In the superconducting state, the material has zero resistance. When the temperature of the material is reduced below the critical temperature, its resistance suddenly reduces to zero. 

3.) Expulsion of Magnetic Field:

• ​Below the critical temperature, superconductors do not allow the magnetic field to penetrate inside them. This phenomenon is called Meisser Effect. 

4.) Critical Magnetic Field:

• The certain value of the magnetic field beyond which the superconductors return to conducting state is called the critical magnetic field.
• The value of the critical magnetic field is inversely proportional to the temperature. 
• As the temperature increases, the value of the critical magnetic field decreases.

5.) Magnetic Susceptibility:

The magnetic susceptibility of an ideal superconductor is -1.

The magnetic field of a superconductor is given by:

B = μ (1 + χ)

where, B = Magnetic field

μ = Permittivity

χ = Susceptibility

SInce, the magnetic field inside a superconductor is zero i.e.

B = 0

0 = μ (1 + χ)

χ = -1

Concept:

• Metal in a superconducting state never allows a magnetic flux density to existing in its interior
• When a superconductor is cooled in a weak magnetic field, at the critical temperature persistent current arises and circulates so as to cancel the magnetic field inside, in just the way as a magnetic field is applied after the metal has been cooled 
• A superconductor never has a flux density even when in applied magnetic fields, which is called the Meissner effect.

Explanation:

The superconductor is characterized in two parts ie., type-1 and type-2 

Thus option 1 is correct.

Additional Information

• The ability of a material to permit the pass of magnetic lines of force through it is known as Permeability and is denoted as (\(\mu\))
• The material they are characterized into 3 parts depending upon the value of relative permeability and they are

Explanation:

There are various types of symbols are used to classify heat treatable plain carbon steel which is listed below in the table.

Explanation:

When two or more metals are mixed together to form metal, it is called an alloy.

Babbitt metal:

• Babbitt metal is a soft, white non-ferrous alloy that is used to provide a bearing surface. 
• Babbitt metal also has properties that help it reduce friction which makes it a good material for use in a plain bearing.
• Babbitt metal is tin and lead-based alloy:

Tin based Babbitt metal: 

• It contains Sn (Tin) = 88%, Sb (antimony) = 8%, Cu (copper) = 4%.
• It possesses excellent anti-friction properties and sufficient mechanical strength, so most commonly used in bearing metal.

Lead-based Babbitt metal: 

• It contains Pb (Lead) = 85%, Sb (antimony) = 10%, Cu (copper) = 5%

Important Points

Here are some alloys and their properties:

Concept:

• The SI unit of the dielectric strength is volts per meter (KV/cm) or MV/cm
• It is also common to see related units as volts per cm(V/cm), megavolts per meter(MV/m)
• Mica is widely known for its high dielectric strength, which is typically around 100–200 MV/cm, depending on the quality and type of mica. A dielectric strength of 0.02 MV/cm (20 kV/cm) is far too low for mica and would not represent its properties as an insulator. Hence, 118 MV/cm is the most appropriate answer.
• Dielectric strength is defined as for a pure electrically insulating material, the maximum electric field that the material can withstand under ideal conditions without undergoing electrical breakdown and becoming electrically conductive (i.e. without failure of its insulating properties)
• The most common dielectric materials include aluminum & tantalum oxide, ceramic, plastic film, polymer, glass, mica, and paper.
• For high-frequency applications, ceramic capacitors are a good option. However, these capacitors have a poor aging performance.
• Mica and glass capacitors are suitable for applications that demand extremely high stability, reliability, and tolerance to high voltages and temperatures. However, these capacitors are typically expensive and are, therefore, not commonly used in low-cost devices.
• Aluminum or tantalum plate capacitors with an oxide dielectric material are widely used for applications that require high capacitance.
• Silicon-based dielectrics such as silicon dioxide and silicon nitride are commonly used in high-density capacitors.
• Capacitors with silicon dielectrics are ideal for applications that demand high stability, reliability, and tolerance to high temperatures.
• The performance characteristics of these capacitors make them a suitable choice for use in harsh environment applications.
   

Strengths of silicon-based dielectrics

1. High stability at high temperature
2. High potential for miniaturization
3. Leakage current stability at high temperature
4. Low failure rate
    

Limitations

• Limited maximum capacitance
• Charge leakage
   

Conclusion:

For more information: https://aximmica.com/micas-dielectric-shock-properties-a-key-to-electrical-safety/

Statement 1:

• Large energy would be required to scatter a huge number of electrons so lattice ions are not able to scatter the electrons and hence due to this resistivity drops to zero.
• So Resistivity of superconductors is zero for temperatures below T_c.
   

Statement 2: Effect of Magnetic Filed on Super-Conductor:

• Diamagnetics have a magnetization that opposes any applied magnetic field, the superconductor is repelled by the magnetic field.
• When a magnet is placed above a superconductor, this repelling force can be stronger than gravity, allowing the magnet to levitate above the superconductor.
   

Statement 3: Barium Ferrite:

• Barium ferrite is a highly magnetic material, has a high packing density, and is a metal oxide.
• Barium ferrite is used in applications such as recording media, permanent magnets, and magnetic stripe cards

Concept:

There are 7 class of insulating materials, each suitable for different application:

The permissible temperature limit at which the insulators may be worked safely without deterioration depends upon the type and class of the insulation as detailed below.