Assignment Problems with Answers

ASSIGNMENT PROBLEMS

1. A copper rod 19 cm long and of 0.785 cm area of (10 cross-section which is thermally insulated is heated at one end to 100°C while the other end is kept at 30°C. Calculate the amount of heat that will flow in 10 minutes along the way. K of copper is 380 Wm^-1 K^-1

(Ans. 6.594 kJ)

2. Two bars of copper and steel of length 1.0 m and 0.5 m respectively and of coefficient of thermal conductivity 400 W m^-1K^-1 and 50 W m^-1 K^-1 respectively are joined end to

end.

The free ends of copper and steel are maintained at 100°C and 0°C respectively. Calculate the temperature of copper-steel junction if both bars have the same area of cross-section.

(Ans. 80°C)

3. Calculate the thickness of the slab of area 85 x 10 m through which 8 joules of heat is flowing through the opposite faes maintained at a temperature difference of 30 K. The coefficient of thermal conductivity of the material of the slab is 0.05 W m^-1 K^-1 .The time taken for the heat flow is 10 seconds

 (Ans. 0.0159 m)

4. Equal bars of copper and aluminium are welded end to end. If the free ends of copper and aluminium are maintained at 150°C and 0°C respectively. Find the temperature of the welded interface. Assume the thermal conductivity of copper and aluminium to be 386.4 W m^-1 K^-1 and 210 W m^-1 K^-1 respectively.

 (Ans. 97.183 °C)

5. A slab consists of two parallel layers of different materials 4 cm and 2 cm thick and of thermal conductivity 226.8 W m^-1 K^-1 and 150.2 W m^-1 K^-1 respectively. If the opposite faces of the slab are at 100°C and 0°C. Calculate the temperature of the surface dividing the two.

(Ans. 316 K or 43°C)

6. The outer ends of two bars A and B (inner ends of which joined together by welding) are at 100°C and 50°C respectively. Calculate the tempearature at the welded joint if they have the same cross section and the same length and their thermal conductivity are in the rate A:B = 7:5. (AU, April 2016)

(Ans: 79.16° C)