This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Properties of Insulation – 2”.
1. The resistance of an insulating material ______ as the temperature increases.
a) Increases
b) Decreases
c) Remains the same
d) Becomes infinitely large
View Answer
Explanation: For insulating materials, the resistivity decreases as the temperature is increased. For metals, however, the resistance increases due to an increase in temperature. This is used as a key characteristic while distinguishing the two.
2. Ionic conductivity of a material can be increased by _______
a) Absorption of water
b) Increase in temperature
c) Increase in length
d) Decrease in temperature
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Explanation: Due to the absorption of water, the ionic conductivity of a material is enhanced due to a chemical reaction. Changes in temperature usually influence the resistance effect of the insulating materials.
3. Cork has a low thermal conductivity of _____ W/m K.
a) 0.01
b) 0.04
c) 0.07
d) 0.1
View Answer
Explanation: Cork is a typical insulating material which has a low thermal conductivity of 0.07 W/m K. This causes the material to be porous in nature. Cotton also has a low thermal conductivity of 0.04 W/m K.
4. The measure of loss of energy in a material is defined as _____
a) Resistivity
b) Dissipation factor
c) Electric strength
d) Conductivity
View Answer
Explanation: Dissipation factor is defined as a measure of loss of energy in an insulating material. When this value is above the standard level, it results in overheating. This may also be caused due to a high value of the frequency of applied voltage or electric field strength.
5. Which of the following is both a good electrical insulator and thermal conductor?
a) Diamond
b) Copper
c) Tin
d) Asbestos
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Explanation: The heat generated by electrical equipment must be dissipated to prevent damage from overheating. Diamond, alumina, beryllia, and magnesia are generally regarded as materials having good electrical insulation as well as thermal conductivity.
6. The insulating materials resist degradation by stability against chemical reaction over ________
a) Temperature and oxygen
b) Temperature and pressure
c) Pressure and density
d) Oxygen and pressure
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Explanation: Oxygen and moisture cause degradation in insulating materials. This can be overcome by the resistance to chemical reaction over temperature and with oxygen. Thermal and oxidation stability are two important chemical properties of insulating materials.
7. Cellular concrete is used for ______ insulation.
a) Thermal
b) Chemical
c) Sound
d) Electrical
View Answer
Explanation: Cellular concrete is a sound insulation material used in the manufacturing stages. It is made by mixing water along with a combination of cement and powdered aluminum.
8. Which insulating material does a combination of magnesium oxychloride and gelatin produce?
a) Pearlite
b) Vermiculite
c) Cellular concrete
d) Acoustic plaster
View Answer
Explanation: Acoustic plaster is a common sound insulation material made by mixing magnesium oxy-chloride granulated slag with gelatin. This can be applied to a wall to create the required insulation by forming a porous layer.
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