Four rods with different radii 'r' and length 'l' are used to connect to reservoirs of heat at different temperature. Which one of them with conduct most heat?

Related MCQs

• Three rods one made of glass, one of pure aluminium and one made of wrought iron are heated to 150?C. All the rods are 15 mm in diameter and 300 mm long. The lowest temperature at the free end of the rods will occur in case of
• The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are
• Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then
• There are two spheres of copper the ratio of their radii being 1 : 3 both at the same temperature. The ration of heat contents will be
• A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,
• A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time
• Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?
• Four identical copper cubes are painted with different paints. Now if all the cubes are heated to the same temperature and are left in vacuum, which cube will lose heat more rapidly? The colours of the cubes are
• A liquid to liquid counterflow heat exchanger is used to heat cold fluid from 50?C to 150?C. Assuming that the hot fluid enters at 250?C and leaves at 200?C, the log mean temperature difference for the heat exchanger will be closer to
• A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is