Heat Transfer Physics - Heat Transfer

A blackbody does not:

1. Emit radiation.
2. Absorb radiation.
3. Reflect radiation.
4. Refract radiation.

One end of a metal rod is dipped in boiling water and the other is dipped in melting ice:

1. All parts of the rod are in thermal equilibrium with each other.
2. We can assign a temperature to the rod.
3. We can assign a temperature to the rod after steady state is reached.
4. The state of the rod does not change after steady state is reached.

In a room containing air, heat can go from one place to another:

1. By conduction only.
2. By convection only.
3. By radiation only.
4. By all the three modes.

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 temperature of the atmosphere at a high altitude is around 500^°C. Yet an animal there would freeze to death and not boil. Explain.

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?

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.

Why is a white dress more comfortable than a dark dress in summer?

An ordinary electric fan does not cool the air, still it gives comfort in summer. Explain.

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?

Four identical rods AB, CD, CF and DE are joined as shown in figure. The length, cross-sectional area and thermal conductivity of each rod are l, A and K respectively. The ends A, E and F are maintained at temperatures T₁, T₂ and T₃ respectively. Assuming no loss of heat to the atmosphere, find the temperature at B.

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.

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.

1.  

2.  

3.  

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.

A rod of negligible heat cafacity has length 20cm, area of cross section 1.0cm and thermal conductivity 200Wm^-1°C^-1. The temperature of one end is maintained at 0^°C and that of the other end is slowly and linearly varied from 0^°C to 60^°C in 10 minutes. Assuming no loss of heat through the sides, find the total heat transmitted through the rod in these 10 minutes.

Steam at 120^°C is continuously passed through a 50cm long rubber tube of inner and outer radii 1.0cm and 1.2cm. The room temperature is 30^°C. Calculate the rate of heat flow through the walls of the tube. Thermal conductivity of rubber = 0.15Js^-1m^-1°C^-1.

A calorimeter contains 50g of water at 50^°C. The temperature falls to 45^°C in 10 minutes. When the calorimeter contains 100g of water·at 50^°0, it takes 18 minutes for the temperature to become 45^°C. Find the water equivalent of the calorimeter.