One end of a metal rod is kept in a furnace. In steady state, the temperature of the rod:
- Increases.
- Decreases.
- Remains constant.
- Is nonuniform.
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Heat Transfer. question types
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33 Q→Sample Questions
Heat Transfer. questions
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A hot liquid is kept in a big room. Its temperature is plotted as a function of time. Which of the following curves may represent the plot?
The thermal conductivity of a rod depends on:
- Length.
- Mass.
- Area of cross section.
- Material of the rod.
A blackbody does not:
- Emit radiation.
- Absorb radiation.
- Reflect radiation.
- Refract radiation.
In summer, a mild wind is often found on the shore of a calm river. This is caused due to,
- Difference in thermal conductivity of water and soil.
- Convection currents.
- Conduction between air and the soil.
- Radiation from the soil.
Standing in the sun is more pleasant on a cold winter day than standing in shade. Is the temperature of air in the sun considerably higher than that of the air in shade?
The temperature of the atmosphere at a high altitude is around 500°C. Yet an animal there would freeze to death and not boil. Explain.
Assume that the total surface area of a human body is 1.6m2 and that it radiates like an ideal radiator. Calculate the amount of energy radiated per second by the body if the body temperature is 37°C. Stefan constant $\sigma$ is 6.0 × 10-8Wm-2K-4.
View full solution →On a cold winter night you are asked to sit on a chair. Would you like to choose a metal chair or a wooden chair? Both are kept in the same lawn and are at the same temperature.
An ordinary electric fan does not cool the air, still it gives comfort in summer. Explain.
Why is a white dress more comfortable than a dark dress in summer?
Does a body at 20°C radiate in a room, where the room temperature is 30°C? If yes, why does its temperature not fall further?
On a hot summer day we want to cool our room by opening the refrigerator door and closing all the windows and doors. Will the process work ?
A semicircular rod is joined at its end to a straight rod of the same material and the same cross-sectional area. The straight rod forms a diameter of the other rod. The junctions are maintained at different temperatures. Find the ratio of the heat transferred through a cross section of the semicircular rod to the heat transferred through a cross section of the straight rod in a given time.
A cylindrical rod of length 50cm and cross sectional area 1cm2 is fitted between a large ice chamber at 0°C and an evacuated chamber maintained at 27°C as shown in figure. Only small portions of the rod are inside the chambers and the rest is thermally insulated from the surrounding. The cross section going into the evacuated chamber is blackened so that it completely absorbs any radiation falling on it. The temperature of the blackened end is 17°C when steady state is reached. Stefan constant $\sigma=6\times10^{-8}\text{W/m}^{-2}\text{K}^{-4}.$ Find the thermal conductivity of the material of the rod.
View full solution →One end of a steel rod $(\text{K}=46\text{Js}^{-1}\text{m}^{-1}{^{\circ}}\text{C}^{-1})$ of length 1.0m is kept in ice at 0°C and the other end is kept in boiling water at 100°C. The area of cross section of the rod is 0.04cm2. Assuming no heat loss to the atmosphere, find the mass of the ice melting per second. Latent heat of fusion of ice $=3.36\times10^5\text{Jkg}^{-1}.$
View full solution →Consider the situation of the previous problem. Assume that the temperature of the water at the bottom of the lake remains constant at 4°C as the ice forms on the surface (the heat required to maintain the temperature of the bottom layer may come from the bed of the lake). The depth of the lake is 1.0m. Show that the thickness of the ice formed attains a steady state maximum value. Find this value. The thermal conductivity of water $=0.50\text{Wm}^{-1}{^{\circ}}\text{C}^{-1}.$ Take other relevant data from the previous problem.
View full solution →One end of a rod of length 20cm is inserted in a furnace at 800K The sides of the rod are covered with an insulating material and the other end emits radiation like a blackbody. The temperature of this end is 750K in the steady state. The temperature of the surrounding air is 300K. Assuming radiation to be the only important mode of energy transfer between the surrounding and the open end of the rod, find the thermal conductivity of the rod. Stefan constant $\sigma=6.0\times10^{-8}\text{Wm}^{-2}\text{K}^{-4}.$
View full solution →Cloudy nights are warmer than the nights with clean sky. Explain.
Consider the situation shown in figure. The frame is made of the same material and has a uniform cross-sectional area everywhere. Calculate the amount of heat flowing per second through a cross section of the bent part if the total heat taken out per second from the end at 100°C is 130J.
The three rods shown in figure, have identical geometrical dimensions. Heat flows from the hot end at a rate of 40 Win the arrangement (a) Find the rates of heat flow when the rods are joined as in arrangement (b) and in (c) Thermal conductivities of aluminium and copper are 200Wm-1°C-1 and 400Wm-1°C-1 respectively. 
Suppose the bent part of the frame of the previous problem has a thermal conductivity of 780Js-1m-1°C-1 whereas it is 390Js-1m-1°C-1 for the straight part. Calculate the ratio of the rate of heat flow through the bent part to the rate of heat flow through the straight part.
An amount n (in moles) of a monatomic gas at an initial temperature T0 is enclosed in a cylindrical vessel fitted with a light piston. The surrounding air has a temperature Ts(> T0) and the atmospheric pressure is Pa· Heat may be conducted between the surrounding and the gas through the bottom of the cylinder. The bottom has a surface area A, thickness x and thermal conductivity K. Assuming all changes to be slow, find the distance moved by the piston in time t.
Why does blowing over a spoonful of hot tea cools it? Does evaporation play a role? Does radiation play a role?
Figure, shows water in a container having 2.0mm thick walls made of a material of thermal conductivity $0.50\text{Wm}^{-1}{^{\circ}}\text{C}^{-1}.$ The container is kept in a melting-ice bath at 0°C. The total surface area in contact with water is 0.05m2. A wheel is clamped inside the water and is coupled to a block of mass M as shown in the figure. As the block goes down, the wheel rotates. It is found that after some time a steady state is reached in which the block goes down with a constant speed of 10cms-1 and the temperature of the water remains constant at 1.0°C. Find the mass M of the block. Assume that the heat flows out of the water only through the walls in contact. Take g = 10ms-2.
View full solution →A composite slab is prepared by pasting two plates of thicknesses L1 and L2 and thermal conductivities K1 and K2. The slabs have equal cross-sectional area. Find the equivalent conductivity of the composite slab.
An icebox almost completely filled with ice at 0°C is dipped into a large volume of water at 20°C. The box has walls of surface area 2400cm2, thickness 2.0mm and thermal conductivity $0.06\text{Wm}^{-1}{^{\circ}}\text{C}^{-1}.$ Calculate the rate at which the ice melts in the box. Latent heat of fusion of ice $= 3.4\times10^5\text{Jkg}^{-1}.$
View full solution →Two bodies of masses m1 and m2 and specific heat capacities s1 and s2 are connected by a rod of length l, cross-sectional area A, thermal conductivity K and negligible heat capacity. The whole system is thermally insulated. At time t = 0, the temperature of the first body is T1 and the temperature of the second body is T2 (T2 > T1). Find the temperature difference between the two bodies at time t.
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