Define heat in terms of K.E. Give its SI unit.
The total sum of kinetic energy contained by the molecules of the body is called the heat energy of that body.
Its SI unit is Joule.
What is meant by calorimetry? State its principle.
Calorimetry is the measurement of heat lost or gained by an object.
The principle of calorimetry state that 'When a hot body is mixed with a cold body, the heat lost by the hot body is equal to the heat gained by the cold body, provided that no heat escapes to the surroundings.'
Therefore, Heat lost = Heat gained.
The difference between heat & temperature are:
|It is the form of energy.||Temperature is the degree of hotness or coldness of a body.|
|It is measured by a caloriemeter.||It is measured by a thermometer.|
|Its SI unit is Joule.||Its SI unit is Kelvin.|
|It is the cause of temperature.||It is the effects of heat.|
We all know that the FP of alcohol is - 1150C and BP is780C. But the FP of mercury is - 350Cand BP is3570C. So, mercury has a normal physical state at 1000Cand can measure temperature. But, alcohol starts boiling if the temperature raised to780C. So, it changes to a gasstate at1000Cand cannot measure temperature. Hence, wecan measure the temperature of1000C with a mercury thermometerbut not with an alcohol thermometer.
The thermometer that is used in labs having the range from -100C to 1100Cis called a laboratory thermometer.
It consists of a thick-walled capillarymade up of glass in which one end is closed and its other end has acylindrical bulb. This bulb and a small portion of the capillary is filled with pure mercury.The air from the tube is completely taken outbefore closing the upper end. The vacuum created bringseasiness in the labeling of temperature.
When any hot body is cooled, it gives out heat, and itstemperature falls. Also, whenany cool body is heated, it absorbsheat, and its temperature rises. It has been proved that heat gained or lost isdirectly proportional to:
Combining 1 and 2, we get:
or, Q = msdt where s is constant called specific heat capacity of the body.
Therefore,Q = msdtis the heat equation.
We know from the principle of calorimetry that the heatgained by a cool body from a hot body is equal to the heatlost by a hot body. To cool the engines, something shouldabsorb its heat and water has the highest capacityto absorb heat as its specific heat capacity 4200J/Kg0C.
So, water is used to cool the engines of machines.
As we all know that water has the highest specificheat capacity. It means that it has the highest capacity of absorbing heat. So, the heated water releases heatfor the longest time. As the hot bottles are used for heating purposes, hot water is used in them.
We know that the density of solid ghee is more than thatof liquid or hot ghee. So while freezing, all the frozenghee starts to displace to the bottom. But, water has a higherdensity at 40C than at 00C. It means water has a higherdensity than ice. So, while freezing, ice displaces tothe top.
We all know that, the temperature of our body higher in the bedroom than the temp. of surrounding. So, when we gooutside, our body loses the heat and we feel cold.
After strolling outside in open air the temp of ourbody again decreases below the temp. of bedroom. So, when we come back to the bedroom, our body gains heat and we feel warm.
We know that in the desert the land is covered all by sand.Sand has low specific heat capacity which means it gainsand loses heat very fast. So, during the day it gains max heat and becomes hotter and during the night it loses all the heat and becomes very cold.
We know that mercury is only the metal that exists inthe state of liquid with a freezing point - 39C andboiling point 357C. The range of its FP and BP is suitablefor measuring normal temp. It is also a goodconductor of heat. It has a low specific heat capacity i.e.140 J/KgC.So, it is usedas a thermometric liquid.
We all know that water has the highest specific heatcapacity. So, it absorbs more heat and also loses moreheat. During the day, the heat near the sea area is absorbedby water in the sea and during the night the area near the seaabsorbs heat from the sea.
So, the temp near the searemains moderate.
In the winter season, the morning temp. on the earth's surface is very low. But the inner core of the earth is always hot. We know, well water is absorbed from deep inside the ground. At that surface, water absorbs the heat from the earth's core and remains hot. When the same water is brought to the surface, the temp. of water is higher than that of surroundings. So, well water is felt to be warmer in the morning during the winter.
A new quilt has high air storage capacity as it is thickerthan the old one, But the old quilt can't store moreair as it is compressed by several uses. So, a new quiltacts as a better insulator than the old one. So, a new quiltprevents our body's heat to be released into the atmosphere in a better way than the old one. Hence, a new quilt is warmer than an old one.
It means one kilogram mass of B requires 470J of heat to raise its temp. by 10C.
C will have the highest temperature because it has the lowest sp. heat capacity and B will have the lowest temperature because it has the highest sp. heat capacity.
From: sp. heat capacity1/temperature.
B will make the deepest hole in the wax slab because it has more heat to release to the wax slab as it is with constant mass and temp. with the highest sp. heat capacity.
The formation of cloud above ocean is due to evaporation, not boiling. And evaporation takes place in any temperature. So ocean water need not to be 100 degree Celsius for forming cloud.