  # ISRO Scientist or Engineer Mechanical 2010

Instructions

For the following questions answer them individually

Question 1

# If thermal conductivity of a material of wall varies as $$k_0(1 - \alpha T)$$, the temperature at the center of the wall will be ($$\alpha$$ is +ve) Question 2

# The spectral emissive power $$E_1$$ ; for a diffusely emitting surface is $$E_1 = 0 for \lambda < 3\mu m; E_1 = 150 W/m^2 \mu m for 3 < \lambda < 12 \mu m; E_1 = 300W/m^2 \mu m for 12 < \lambda < 25 \mu m; E_1 = 0 for \lambda > 25 \mu m.$$ The total emissive power of the surface over the entire spectrum is Question 3

# A wire is plastically deformed bent by supplying a force of 40 N over a distance of 0.8 m. (The force moves in the direction in which the distance is measured). If the wire has a mass of 0.2 kg and a specific heat of $$0.5 kJ/kg.^\circ C$$ estimate the maximum increase in the average temperature of the wire Question 4

# Two rods one of length L and the other of length 2L are made of the same material and have the same diameter. The two ends of the longer diameter. The two ends of the longer rod are maintained at $$100^\circ C$$. One end of the shorter rod is maintained at $$100^\circ C$$ while the other end is insulated. Both the rods are exposed to the same environment at $$40^\circ C$$. The temperature at the insulated end of the shorter rod is measured to be $$55^\circ C$$. The temperature at the midpoint of the longer rod would be Question 5

# A sphere, a cube and disc all of the same material, quality and volume are heated to 900 K and left in air. Which of these will have the lowest rate of cooling Question 6

# Air with initial condition of p1,vl expands to final condition of $$p1/2, 3v_1.$$ The process is Question 7

# Sun’s surface at 5800 K emits radiation at a wavelength of $$0.5\mu A$$ furnace at $$300^\circ C$$ will emit through a small opening, radiation at a wavelength of Question 8

# Polytropic index x is given by Question 9

# The heat flow rate through parallel walls of thickness $$L_1, L_2, and L_3$$ and having surface areas $$A_1, A_2, and A_3$$, thermal conductivities $$k_1, k_2, and k_3,$$ respectively and first and last walls maintained at temperatures $$t_1 and t_2$$ will be Question 10

# Which of the following property of air does not increase with rise in temperature? OR