E-PolyLearning

31. A cylindrical cement tube of radii 0.05 cm and 1.0 cm has a wire embedded into it along its axis. To maintain a steady temperature difference of 120 degree Celsius between the inner and outer surfaces, a current of 5 ampere is made to flow in the wire. Find the amount of heat generated per meter length. Take resistance of wire equal to 0.1 ohm per cm of length
a. 150 W/m length
b. 250 W/m length
c. 350 W/m length
d. 450 W/m length
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Answer: (b).250 W/m length

32. A stainless steel tube with inner diameter₁2 mm, thickness 0.2 mm and length 50n cm is heated electrically. The entire 15 k W of heat energy generated in the tube is transferred through its outer surface. Find the intensity of current flow
a. 52 amps
b. 62 amps
c. 72 amps
d. 82 amps
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Answer: (a).52 amps

33. The temperature distribution associated with radial conduction through a sphere is represented by
a. Parabola
b. Hyperbola
c. Linear
d. Ellipse
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Answer: (b).Hyperbola

34. The thermal resistance for heat conduction through a spherical wall is
a. (r₂-r₁)/2πkr₁r₂
b. (r₂-r₁)/3πkr₁r₂
c. (r₂-r₁)/πkr₁r₂
d. (r₂-r₁)/4πkr₁r₂
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Answer: (d).(r₂-r₁)/4πkr₁r₂

35. The rate of conduction heat flow in case of a composite sphere is given by
a. Q = t₁ – t₂/ (r₂ – r₁)/4πk₁r₁r₂ + (r3 – r2 )/4πk₂r₂r₃
b. Q = t₁ – t₂/ (r₂ – r₁)/4πk₁r₁r₂ + (r3 – r2 )/4πk₂r₂r₃
c. Q = t₁ – t₂/ (r₂ – r₁)/4πk₁r₁r₂ + (r3 – r2 )/4πk₂r₂r₃
d. Q = t₁ – t₂/ (r₂ – r₁)/4πk₁r₁r₂ + (r3 – r2 )/4πk₂r₂r₃
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Answer: Q = t₁ – t₂/ (r₂ – r₁)/4πk₁r₁r₂ + (r₃ – r₂ )/4πk₂r₂r₃