Questions and answers for exam Preparation

MCQs

Total Questions : 70 | Page 5 of 7 pages

Question 41. With respect to the equation k = k0 (1 +β t) which is true if we put β = 0?

Slope of temperature curve is constant
Slope of temperature curve does not change
Slope of temperature curve increases
Slope of temperature curve is decreases

Discuss Question

Answer: Option A. -> Slope of temperature curve is constant
Answer: (a).Slope of temperature curve is constant

Question 42. The unit of thermal conductivity doesn’t contain which parameter?

Watt
Pascal
Meter
Kelvin

Discuss Question

Answer: Option B. -> Pascal
Answer: (b).Pascal

Question 43. The temperatures on the two sides of a plane wall are t1 and t2 and thermal conductivity of the wall material is prescribed by the relation
K = k0 e^(-x/δ)
Where, k0 is constant and δ is the wall thickness. Find the relation for temperature distribution in the wall?

t 1 – t x / t 1 – t 2 = x
t 1 – t x / t 1 – t 2 = δ
t 1 – t x / t 1 – t 2 = δ/x
t 1 – t x / t 1 – t 2 = x/δ

Discuss Question

Answer: Option D. -> t 1 – t x / t 1 – t 2 = x/δ
Answer: (d).t 1 – t x / t 1 – t 2 = x/δ

Question 44. If β is greater than zero, then choose the correct statement with respect to given relation
k = k0 (1 +β t)

k doesn’t depends on temperature
k depends on temperature
k is directly proportional to t
Data is insufficient

Discuss Question

Answer: Option C. -> k is directly proportional to t
Answer: (c).k is directly proportional to t

Question 45. “If β is less than zero, then with respect to the relation k = k0 (1 + β t), conductivity depends on surface area”. True or false

True
False
May be
Can't say

Discuss Question

Answer: Option B. -> False
Answer: (b).False

Question 46. An electric cable of aluminum (k = 240 W/ m degree) is to be insulated with rubber (k = 6 W/ square meter degree). If the cable is in air (h = 6 W/square meter degree). Find the critical radius?

80 mm
160 mm
40 mm
25 mm

Discuss Question

Answer: Option D. -> 25 mm
Answer: (d).25 mm

Question 47. The value of critical radius in case of cylindrical hollow object is

2k/h
2h/k
k/h
h/k

Discuss Question

Answer: Option C. -> k/h
Answer: (c).k/h

Question 48. A pipe of outside diameter₂0 mm is to be insulated with asbestos which has a mean thermal conductivity of 0.1 W/m degree. The local coefficient of convective heat to the surroundings is 5 W/square meter degree. Find the critical radius of insulation for optimum heat transfer from pipe?

10 mm
20 mm
30 mm
40 mm

Discuss Question

Answer: Option B. -> 20 mm
Answer: (b).20 mm

Question 49. A wire of radius 3 mm and 1.25 m length is to be maintained at 60 degree Celsius by insulating it by a material of thermal conductivity 0.175 W/m K. The temperature of surrounding is 20 degree Celsius with heat transfer coefficient 8.5 W/ m² K. Find percentage increase in heat loss due to insulation?