1st year physics notes ch10
The correct answers with their questions numbers see complete question in your book.
1 = A , 2 = B , 3 = D , 4 = A , 5 = B , 6 = A , 7 = A , 8 = D , 9 = A , 10 = B
1st year physics notes ch10 McQS end.
Question 1 Answer: Thermal equilibrium will exist between two bodies, if heat loss by one body is absorbed by the second body. Due to very high temperature, fusion reactions takes place at sun surface and as a result tremendous amount of heat energy is produced. The earth is not a good absorber. It absorbs some part of energy loss by sun. Also during night, the earth radiate some heat back into the atmosphere. That is why the earth is not in thermal equilibrium with the sun.
Question 2 Answer: As the black is heated, all the dimensions increases, including the diameter of the hole. A useful analogy to thermal expension is that of photographic anlargment. Every linear dimension of the object underrgoes the same fractional change. Thus the increase in temperature will expand the hole and will not reduce it.
Question 3 Answer: A thermometer registers its own temperature. When a thermometer is in thermal contact with an object , the temperature of which we wish to measure , energy will flow between the two until their temperature becomes equal and thermal equilibrium is established. At this stage, the temperature of thermometer will gives us the temperature of the body. A thermometer placed in direct sun light is in more contact with the surrounding air, so it will read the temperature of the air.
Question 4 Answer: According to Graham’s law of diffusion, the rate of diffusion of a certain gas is inversely proportional to its molecular mass and density i-e smaller the molecular mass and density, greater will be the rate of diffusion and vice versa. As the hydrogen is lighter than oxygen i-e its molecular mass and density is lower than that of oxygen, so the pressure in a gas cylinder containing hydrogen will leak more quickly than if it is containing oxygen.
Question 5 Answer: The air conditioner is placed in the middle of the room, so the absorption and rejection of heat energy take place in the same room. As a result there will be no change in the temperature of the room.
Question 6 Answer: A- When a sealed thermos flask bottle full of hot coffee is shaken, then the kinetic energy of the molecules of the coffee increases and thus the temperature of the coffee will increase.
B- When a sealed thermos flask bottle full of heat coffee is shaken, the kinetic energy and temperature of molecules of the coffee increases. As such activity is an adiabatic process, so the internal energy will increase.
Question 7 Answer: When an object is heated, not all the energy it absorbs goes into increasing the velocity of the molecules. Some part of supplied heat energy is used agianst frictional effects among molecules and same part is used to increase the potential energy of molecules of the object.
Question 8 Answer: When an autumobile is driven for a while , work is done against the frictional effects between tyre and road. As a result , heat energy is produced due to which the temperature of tyre and air inside it increases. As a result the collision of air molecules with each other and with the walls of the tyre increase and hence the pressure of air inside the tyre increases.
Question 9 Answer: The air inside cycle tube is at high pressure and high temperature. When the value is removed , the air rushes out from the tube. the outside atmospheric pressure is less than the air pressure inside the tube. As a result, the temperature of air falls down and hence becomes cool.
Question 10 Answer: A refrigerator is a device which operates in the reverse order of a heat engine. that is it extract heat from a cold body and transfer it to a hot body. No refrigerator is 100% efficient. Thus it exhausts more heat into the room than it extract from it. Therefore, the net effect is an increase in the temperature of the room and it can not be cooled by opening the door of the refrigerator inside the room.
Question 11 Answer : A- The system should be very nearly in equilibrium.
B- There should no fractional effect.
C- The process will occur very slowly.
1st year physics notes ch10 short question end.