Conceptual Questions | Chapter 8 | Heat & Thermodynamics | Physics 11th | National Book Foundation

Click on the link below for latest videos. https://whatsapp.com/channel/0029VaGr... 8.1 Estimate the total number of air molecules (inclusive of oxygen, nitrogen, water vapour and other constituents) in a room of capacity 𝟐𝟎.𝟎𝒎^𝟑 at a temperature of 𝟐𝟕℃ and 𝟏𝒂𝒕𝒎 pressure. 8.2 A sample of gas is compresses to one third of its initial volume at constant pressure of 𝟐.𝟐𝟓×〖𝟏𝟎〗^𝟓 𝑵/𝒎^𝟐. During the compression, 𝟐𝟎𝟎𝑱 on work is done of the gas. Determine the final volume of the gas. 8.3 A cup is filled with hot tea with a spoon for string purpose. Initially the tea has an internal energy of 𝟐𝟎𝟎𝒌𝑱, and while cooling it loses 𝟏𝟓𝟎𝒌𝑱 of heat. The spoon does 𝟐𝟓𝒌𝑱 of work while stirring. Find the change in internal energy of the tea and the final internal energy of the tea. 8.4 A heat engine is working with thermal efficiency of 40%. It receives 𝟒𝒌𝑱 of heat from furnace, what waste heat does it reject? 8.5 The temperature inside a refrigerator is 𝒕_𝟐℃ and the room temperature is 𝒕_𝟏℃. Find the amount of heat delivered to the room for each joule of electricity consumed ideally. 8.6 A body 𝟏𝟓𝟎℃ undergoes a reversible isothermal process. The heat energy removed in the process is 𝟕𝟑𝟕𝟑𝑱. Find the entropy change of the body. In 60℉ walking on the ground weather feels comfortable, but swimming in ocean feels very cold. Explain. Do you think low temperature is the only reason for snowfall on mountains? Can the temperature of an isolated system change? Explain. As a result of some process, the internal energy of a system is increased. How can one tell that the increase was due to orderly macroscopic work W or due to the flow of disorderly microscopic energy ’Q’? At what temperature (in ℃) the volume of a gas at 0℃ becomes double its volume, while pressure remains constant? Work done on system puts energy into it. Work done by system removes energy from it. Give examples? Should the internal energy of a system necessarily increase if heat is added to it? Why the slope of adiabatic curve is steeper than the slope of isothermal curve? What are the limitations of the first law of thermodynamics? What are the conditions for isothermal process? Why isothermal processes are slow and adiabatic processes are fast? Can a process be both adiabatic and isothermal? Explain. Does the entropy increase for a Carnot engine for each cycle? Why in practical terms efficiency is defined as W/Q_h? Does entropy of the system increases or decreases due to friction? What are the similarities and dissimilarities in working of refrigerator and air conditioner? What is meant by reverse entropy? And what is significance of entropy? Explain. What is the difference between heat transfer and thermodynamics? The coffee filled in a thermos is vigorously shaken (i) Has any work been done on coffee? (ii) Does the internal energy of coffee increase? (iii) Does temperature of coffee rise? (iv) Does coffee get heat from outside? A system undergoes from state P_1 V_1 to state P_2 V_2 as shown in figure here. What will be the change in internal energy? What are the conditions for thermodynamic equilibrium? When internal energy of a system rises, can its temperature stay the same? When a car driven certain distance, why does the gas pressure increase in the tires rise? Prove that area under P-V graph is equal to work done. All the reactions going on in the refrigerator are isothermal. Explain? Define reversible, irreversible and cyclic processes. Find number of moles of air in an inflated balloon of radius 10cm and pressure 180kPa at room temperature. Data: A heat engine works between freezing and boiling point of water. Find its efficiency. One mole of a perfect gas in a cylinder fixed with a piston has pressure P, volume V and temperature T. If its temperature is increased by 1K. Find the increase in volume, if initial volume was 100m^3. The high temperature of Carnot engine is 600K. If engine absorbs 600J of heat at low temperature of 400K. Find the work done by the engine. A small 220 watt electric immersion heater is used to boil 136g of water. Calculate the time required to bring this water from 23.5℃ to boiling point, ignore any heat loss. If a heat engine at room temperature gives efficiency 50%, you change the heat source to increase the efficiency upto 70%. Find the temperature difference between the two heat sources. A Carnot engine absorbs an amount Q of heat at temperature T. Find the rejected heat at temperature T/3. 500J energy is required to melt 2g of ice at 0℃. Find the change in entropy of 70g water at 0℃, if it changes into ice in a refrigerator.