Building Construction Multiple Choice Questions & Answers (MCQs) on “Thermal Insulation”.
1. According to Indian Standards, it is recommended that the overall thermal transmittance of a roof should not be more than _______ kcal/m2 h deg C.
a) 2.00
b) 5.00
c) 7.00
d) 9.00
Answer: a
Clarification: According to Indian Standards, it is recommended that the overall thermal transmittance of a roof should not be more than 2.00 kcal/m2 h deg C. It is also recommended that the thermal dampness of a roof should be less than 75%.
2. The process of direct transmission of heat through a material is known as __________
a) Conduction
b) Radiation
c) Thermal insulation
d) Thermal energy
Answer: a
Clarification: The process of direct transmission of heat through a material is known as conduction. The amount of heat transfer by this process depends on various factors like temperature difference, the conductivity of the medium, the time for which the flow takes place etc.
3. Thermal insulation keeps the room cool in winters and hot in summers.
a) True
b) False
Answer: b
Clarification: Thermal insulation keeps the room hot in winters and cool in summers which results in comfortable living. It minimises heat transfer and helps in saving fuel to maintain the desired temperature in the room.
4. The amount of heat flow through a unit area of material of unit thickness in one hour, when the temperature difference is maintained at 1°C is known as ___________ of the material.
a) Thermal conductivity
b) Thermal resistivity
c) Thermal conductance
d) Thermal resistance
Answer: a
Clarification: The amount of heat flow through a unit area of material of unit thickness in one hour, when the temperature difference is maintained at 1°C is known as the thermal conductivity. It is denoted by k. Its units are W/(mK).
5. The reciprocal of thermal conductivity is known as __________
a) Thermal conductance
b) Surface resistance
c) Specific conductance
d) Thermal resistivity
Answer: d
Clarification: The reciprocal of thermal conductivity is known as thermal resistivity. It is given by 1/k. Its units are (mK)/W.
6. Which of the following is the correct relationship between thermal resistance and thermal conductivity?
a) R = k/L
b) R = k.L
c) R = L/k
d) R = L2/k
Answer: c
Clarification: Thermal resistance and thermal conductivity are related by the equation R = L/k. Here, R is the thermal resistance, k is the thermal conductivity and L is the thickness. Thermal resistance is the reciprocal of thermal conductance.
7. Surface resistance is the reciprocal of __________
a) Surface coefficient
b) Surface resistivity
c) Surface conductance
d) Surface conductivity
Answer: a
Clarification: Surface resistance is the reciprocal of the surface coefficient. It is given by 1/f where f denotes the surface coefficient. Its units are (m2K)/W.
8. Thermal damping is given by the equation D = (T-t/T) x 100. Here, T denotes _________
a) Outside temperature range
b) Inside temperature range
c) Total outside and inside temperature range
d) Thickness
Answer: a
Clarification: Thermal damping is given by the equation D = (T-t/T) x 100. Here, T denotes outside temperature range and t denotes inside temperature range. Also, thermal damping is denoted by D.
9. Which of the following is the correct relation between thermal transmittance and thermal time constant?
a) T = Q x U
b) T = k/U
c) T = Q/U
d) T = U/Q
Answer: c
Clarification: Thermal transmittance and thermal time constant are related by the equation T = Q/U. Here, T denotes the thermal time constant, U is the thermal transmittance and Q is the quantity of heat stored.
10. Which of the following is not a quality of a good thermal insulating material?
a) It should be durable
b) It should have a low thermal resistance
c) It should be readily available
d) It should be fireproof
Answer: b
Clarification: A good thermal insulating material should be durable. It should have high thermal resistance. It should be fireproof and readily available.
11. Reflective sheet materials used as thermal insulating material have ___________ reflectivity and __________ emissivity.
a) High, high
b) High, low
c) Low, low
d) Low, high
Answer: b
Clarification: Reflective sheet materials used as thermal insulating material have high reflectivity and low emissivity. Because of this property, it offers high heat resistance.
12. Thermal insulation of roofs can be obtained by covering the top exposed surface of the roof with ________
a) 2.5 cm thick layer of mud mortar
b) 2.5 cm thick layer of coconut pitch cement concrete
c) 7.5 cm thick layer of mud mortar
d) 7.5 m thick layer of coconut pitch cement concrete
Answer: b
Clarification: Thermal insulation of roofs can be obtained by covering the top exposed surface of the roof with 2.5 cm thick layer of coconut pitch cement concrete. Coconut pitch cement concrete is prepared by mixing coconut pitch with water and cement.
13. Presence of moisture in the thermal insulating material increases thermal insulation while the presence of air spaces decreases thermal insulation.
a) True
b) False
Answer: b
Clarification: Presence of moisture in the thermal insulating material decreases thermal insulation while the presence of air spaces increases thermal insulation. The choice of the thermal insulating material depends on various factors like cost of material, area to be covered, coat of heating or cooling, etc.
14. According to the Indian Standards, it is recommended that thermal damping of a wall should not be less than _______
a) 40%
b) 50%
c) 60%
d) 80%
Answer: c
Clarification: According to the Indian Standards, it is recommended that the thermal damping of a wall should not be less than 60%. Hence, it is also recommended that the thermal time constant should not be less than 16 h.
15. According to Indian Standards, overall thermal transmittance of a wall should not be more than __________ kcal/m2 h deg C.
a) 1.3
b) 2.2
c) 3.7
d) 4.6
Answer: b
Clarification: According to Indian Standards, overall thermal transmittance of a wall should not be more than 2.2 kcal/m2 h deg C. Heat insulation of exposed walls can be achieved by increasing the thickness of the wall.