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41. It is possible to seal a piece of Platinum wire into a glass tube but not a piece of brass or iron. Why?

As the linear expansivities of platinum and glass are nearly equal, they expand and contract equally at the same rate. But, the linear expansivity of of the iron or brass is much more greater than that of the glass so, they do not expand and contract at the same rate. Hence, it is possible to seal a piece of platinum wire into a glass tube but not a piece of brass or iron.

 

42. How is it possible to loosen caps on certain bottles by dipping the caps briefly in hot water?

When any substance is heated, it undergoes expansion. Similarly, a cap when dipped in hot water then the cap undergoes expansion. This will slightly heat the bottles also, but they are made of glass and they expand less, compared to the expansion of caps. The caps will then become loosened and it would be easier to uncork them.

 

43. Why does a jammed stopper of glass bottles come out easily when its neck is heated?

When a neck of jammed stopper of glass bottles is heated then due to the thermal energy supplied, it undergo thermal expansion which results in the increment of the cross sectional area of the stopper. Due to this increase in the cross sectional area of the stopper, it is easily to take out a jammed stopper of glass bottles as the mouth of the bottle becomes slightly wider than before. Hence, a jammed stopper of glass bottles comes out easily when its neck is heated.

 

44. Why do marine animals live deep inside a lake when the surface of the lake freezes?

Due to the phenomena of anomalous expansion of water, marine animals are able to live inside a lake when the surface of the lake freezes. As the temperature of water on the surface of lake reaches at 40C then it becomes denser and sinks to the bottom and water from bottom moves upward to the surface. The circulation of water stops when the bottom of lake reaches at temperature of 40C and the surface water freeze at 00C. The frozen water or ice, being less denser than water, floats on the surface of lake and acts as an insulator of heat that doesn't allow the further heat to escape from the pond and to transfer the cold temperature of outside (atmosphere). Due to the absence of circulation of water, water at the bottom of lake remains at constant temperature i.e. 40C and is unlikely to cool further. Hence, the cold-blooded animal can easily survive at temperature ranges between 10C to 40C. Hence, marine animals are able to live deep inside lake when the surface of the lake freezes.

 

45.  Water taps burst in winter in cold countries. Explain why?

During winter in cold countries, temperatures fall well below 4 0C. So due to the very cold temperature the water pipes undergo contraction in length as well as in diameter but water inside the pipes cool, undergoing expansion due to the property of anomalous expansion. On the contrary, pipes shrink. Besides, some water might freeze into ice, causing further expansion (Ice covers greater volume than water). Had there been water only, they could flow to other regions for the adjustment of pressure. But once ice starts to form, they start blocking the flow of water at several locations, changing the pipes into several compressed chambers. The cold water then exerts strong pressure on the walls of pipes, resulting in the bursting of water taps.

 

46. Explain why deserts are sandy?

As the weather is very hot during the day and very cold during the night in the deserts, the rocks expands during the day and contracts during the night. The continuous expansion and contraction process taking place for a long period of time results in the breakage of the rocks into small pieces, resulting in the formation of sands. This is one of the natural phenomenon of formation of sands from the rock. Hence, deserts are sandy. 

 

47. When will a gas have zero specific heat?

The expression for the specific heat capacity of a substance is given by

where Q is the amount of heat provided, m is the mass of the substance and 'θ' is the change in temperature.

According to the expression, if the amount of heat going into a system or coming out of a system can be made equal to zero but some change of temperature can be induced, the value of the specific heat capacity can be made equal to zero. This can be achieved in an adiabatic process, which by definition means the process in which no heat exchange occurs. If, a gas system is compressed adiabatically, the work done from outside on to the gas adds up to its internal energy and so increases the temperature, whereas if it is allowed to expand adiabatically, the energy required to perform work on the outside substances is extracted from the internal energy itself, causing reduction in the internal energy and so fall in temperature. (Remember dU = -PdV)

 

48. Why is water taken as the hot substance in hot water bag (or bottle)?

The specific heat capacity of water is 4200 J/kg 0C, which is higher than any other common liquids. than any other liquid. So, when water cools through a certain range, large amount of heat energy will be released compared to same volume of any other liquid. The purpose of a water bag is to deliver as large amount of heat energy as possible out of certain amount of material. So water is preferred over others.

Besides, due to high value of specific heat capacity, water cools very slowly, giving the same level of warmth for a longer period. Others would remain hot for a very short time and then start cooling off, which is not the expected characteristic from a water bag.

 

49. If 1 kg of iron and 1 kg of lead are both heated to 1000C and placed on ice, the iron sinks more ice than lead. Why?

The sinking of iron or lead piece in ice is related to how much ice can they respectively melt when placed on ice. As the specific heat capacity of iron is greater than that of lead so, if 1kg of iron and 1 kg of lead heated at 1000C are placed on ice, iron releases more heat energy than lead (to cool at 00C from 1000C). So more ice is melted by the iron than lead. Hence, the iron sinks more ice than lead.

 

50. When will a gas have infinite specific heat?

The expression for the specific heat capacity of a substance is given by

where Q is the amount of heat provided, m is the mass of the substance and θ is the change in temperature.

In order to have an infinite specific heat capacity (theoretically at least), there should be no rise in temperature when heat energy is given to a substance or in reverse, there should be no fall in temperature when heat energy is extracted from it. This occurs when a solid melts into liquid or a liquid vaporizes, or just the reverse. So during Fusion, Vaporization, Freezing and Condensation  specific heat capacity of a substance is infinite.

 

51. What is meant by the statement that specific heat of copper is 0.1?

The specific heat of copper is 0.1 means that the amount of heat required to raise the temperature of 1 gram of copper through 10C is 0.1 times the amount of heat required to raise the temperature of 1 gram of water through 10C.

 

 

52. Why do animals eat more in winter?

 

During winter, the rate of heat lost from the body of animals increases according to the Newton's law of cooling (since temperature difference between their body and the atmosphere is large). Hence, due to the loss of heat energy, they have to compensate that energy, they have to have some input, which occurs in the form of food. Consumption of more food increases the production of heat in the body, which compensates the energy lost.

 

 

53. What is water equivalent?

Water equivalent of a given mass of the substance is defined as the mass of water of which change in temperature is same as in the substance by the same amount of heat. It is denoted by w and is defined as

                 w = ms

where, m is the mass of the substance and s is its specific heat. Its unit is gram. It is a quantity defined to make certain calculations easier and faster.

 

54. What should be the specific heat capacity of a thermometer bulb?

The function of a thermometer bulb is to house the mercury and also to transfer any heat energy located outside to the inside of the thermometer as quickly as possible (so that the thermometer can respond quickly and properly). In this regard, it is only possible if the bulb itself heats up quickly. This is further possible only when the bulb is a good conductor of heat and it has less specific heat capacity (because substances with less specific heat capacities get hot and cold faster).

 

55. Why is water used in cooling the engines?

Water possesses high specific heat capacity. So it requires large amount of heat energy to raise its temperature and on the contrary, it also releases a lot of heat energy to cool. When hot substances throw their heat energy to it, it can absorb maximum amount of energy but it still remains cool, and able to absorb more heat (Remember, 1 kg of water eats up 4200 J of heat energy to raise its temperature by a mere 1 0C). So it always is able to absorb large amount of heat energy without itself changing giving the cooling effect to the other substance. Hence, water is used in cooling the engines as well as other substances.

 

56. Water in earthen pot remains cold in summer. Explain why?

As the earthen pot contains large number of small pores that behaves as a capillary tube through which water goes out and evaporates due to the hot temperature during summer. For evaporation, it takes the heat as the latent heat of vaporization from the water in the pot which gives cooling effect to water remained in the pot.

 

57. How is it that ice cream appears cooler to the mouth than the ice at 00C?

Ice cream has a lot of foreign substances added to it, in order to give flavor and for preservation, which decreases its freezing point. So it has to be cooled below 0 0C to form. On the other hand pure water forms ice at 0 0C. Such a substance (icecream) needs more heat energy to change in the liquid state as compared to that of the ice at 0 0C due to the difference in the freezing and melting points. Thus, the ice cream absorbs more heat to change its state than the ice at 0 0C. Hence, ice cream is able to absorb more heat as latent heat from mouth, giving a stronger cooling effect than ice at 0 0C. Hence, ice cream appears cooler to the mouth than ice.

 

 

58. Is it possible to heat substance without rise in temperature?

Generally, the heating of substance is possible without rising its temperature only for a short period during when the substance changes its state i.e. when a substance boils or melts. During the change of state, its temperature remains same (or constant) for a short period so, the heat given to a substance is used to increase spacing between the molecules (by cracking the bonds, of course!) that results in the change of state of that substance. Hence, it is possible to heat substance without rising its temperature.

 

 

59. Why can you get more severe burn from steam at 1000C than from water at 1000C ?
Steam at 1000C contains heat energy equal to the sum of the heat energy of water at 1000C plus the latent heat of vaporization of water because formation of steam is possible only after adding that much amount of energy to water at 1000C. This occurs at the rate of extra 540 calories per gram (or 3.36106 Joules/kg). So, steam at 1000C is more energetic than water at 1000C. Therefore, more heat flow to the body from steam than from water of the same temperature if they are touched. Hence, the result is a feeling of severe burn from steam at 1000C than from water at 1000C.

 

60. Why is an ice at 00C more effective in cooling a drink than water at 00C ?

As an ice absorbs more heat as compared to that of the water due to the property of latent heat of fusion of ice. As a result, it absorbs more heat and change its state to water at 00C first and then it give same effect of cooling as than done by the water at 00C. Hence, due to latent heat of fusion, an ice absorbs more heat as compared to that absorb by water of the same temperature. So, an ice at 00C is more effective in cooling than water at 00C.

 

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