This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Properties of Insulation – 1”.
1. Which of the following is a requirement for thermal insulation in materials?
a) High specific gravity
b) High specific heat
c) Low thermal conductivity
Explanation: Thermal resistance of a material is the property which resists the flow (or rate of flow) of heat in a material. For a material to be a good thermal insulator, it must have low thermal conductivity. Other requirements of thermal insulators are low specific gravity and specific heat, along with being fire and vibration resistant.
2. How does moisture affect the thermal insulation of a body?
d) Becomes zero
Explanation: The thermal conductivity of water is largely greater than that of air. Due to this, the thermal insulation if the material is reduced by a large amount. Therefore, it is preferred that thermal insulators be generally resistant to moisture.
3. Which of the following is an example of organic insulating material?
Explanation: Thermal insulation materials are classified as either organic or inorganic. Silk, wool, wood-pulp, and sawdust are a few examples of organic materials. Some common inorganic insulating materials are glass wool, slag, charcoal, and coke powder.
4. An insulating material named 85% magnesia can be used up to temperatures of _______
Explanation: 85% magnesia is a commonly used insulating material for industrial applications. It contains 85% magnesium carbonate along with 15% asbestos fiber. It can be used for covering surfaces up to 315oC.
5. An insulating material made from ______ is preferred for applications where vibration resistance is vital.
b) Magnesium carbonate
c) Rock wool
d) Cattle hair
Explanation: Sometimes cheaper alternatives are required for insulating applications. One such material is made from cattle hair and is chemically cleaned and felted. It can be used up to a temperature of 107oC and is used to withstand vibration and rough use.
6. A cork insulation with a waterproof binder is used for _______ surfaces.
Explanation: Some insulating materials are used for reducing the amount of heat in a cold storage plant. In such cases, cork insulation (or rock wool) infused with a waterproof binder is used for the insulation.
7. Which of the following is a cause for an increase in insulation?
a) Increase in thickness
b) Decrease in thickness
c) Decrease in cost
d) Low density
Explanation: Generally, as the thickness of material increases, the rate of flow of heat decreases due to which the insulation takes place. This may lead to an increase in cost, but is not the main cause for such a response.
8. An electrically insulating material has a resistivity that is ____ times greater than that of copper.
Explanation: An electrical insulator resists the flow of current due to which it is considered as a poor conductor. A usual material has a resistivity that is just about 1021 bigger than that of copper. Common electrical insulating materials are air, glass, and polyethylene.
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