Physics on Temperature and Heat Essay

Introduction

A temperature in simple terms is described as the core for our sensation to hot or cold, while in Physical terms it is said that the temperature of a substance is relative to the regular kinetic energy of the atoms and molecules in the substance. It is quantified using three different scales namely Kelvin, Celsius and Fahrenheit. The standard scale is the Kelvin scale which uses the least possible temperature which is totally zero at its point of start. Heat in simple terms can be described as the measure of being hot and in Physical terms as a type of energy that can be transmitted from one entity to another. This paper explains various aspects of the physics behind temperature and heat.

Is your time best spent reading someone else’s essay? Get a 100% original essay FROM A CERTIFIED WRITER!

Save 25%

Heat and how it can be transferred

Heat is a type of energy which is transferable from one body to another (Ostdiek and Bord). The transfer of heat from or to a certain substance is simply a way to change the temperature of the substance. This transfer takes place in a scenario where there is a significant difference in temperature between unlike substances or between different segments of a particular substance. This heat can be transmitted in three different mechanisms namely: Conduction, convection, and radiation.

Conduction occurs when heat is transferred from atom to atom or molecules to molecules which are in close contact. This means that the atoms or the molecules in the substance with a higher temperature transmit energy directly to the atoms or molecules in the substance with lower temperature. Therefore the exact point where conduction takes place is the borderline between the two substances where the atoms and molecules collide directly. An example of conduction is when one puts a cold pan on a cooking stove, after a few seconds the pan becomes very hot to match the temperature of the cooking stove. Different substances conduct heat differently. Substances like wool and fiberglass in which heat moves slowly are called thermal insulators while metals are very good conductors (Eckert, Georg, and Drake Jr).

Convection is simply the transmission of heat in fluids. The mechanism behind this is that when a fluid is exposed to high temperatures, it undergoes thermal expansion which makes its density to reduce causing it to move up. This results in mixing of the fluid thus the heat is distributed to all parts of the fluid (Eckert, Georg, and Drake Jr). An exemption to this mechanism is water whose temperature is below 4. An example of the application of convention is heating a room using a heater where air close to the heater is heated thus reducing its density causing it to move up and its atoms to collide with the atoms of cold air thus transferring the heat. Other applications of convection include the occurrence of sea breezes and the stirring of fluids with different temperatures so that they mix.

Radiation is the transmission of heat by the use of electromagnetic waves (Eckert, Georg, and Drake Jr). This is observed when one feels the heat from the sun and in occasions where on uses heat from a hot fire to warm himself or herself. The heat that is transmitted via radiation is interrelated to the radio waves and also to the X-rays which are commonly used in hospitals. A unique property of this type of heat transfer mechanism is that it can take place in a vacuum and this is seen in the case of the sun's heat.

Thermal expansion

Thermal expansion in physical terms is the propensity of matter to modify its shape and volume when exposed to changes in temperature. This can be explained in that when a substance is heated, the kinetic energy of its molecules tends to increase (Ostdiek and Bord). Substances which have not been guarded or limited tend to increase in volume when their temperatures are amplified. Applications of this statement can be seen in the air balloons which tend to increase in size when the air inside them is heated. This can also be seen when a thermometer is placed in a liquid with high temperature, the mercury in the tube will expand.

Expansion of substances occurs because, at elevated temperatures, molecules in a fluid or atoms in a solid substance tend to vibrate over a very large distance causing them to thrust each other apart. In gases, this scenario is greatly evident because the speed of their movement increases with the rising temperatures. Thermal expansion takes place in all dimensions as in the case of heating a brick where the length of the brick, its thickness and also its width all increase in equal proportions. This three dimensional increase (l) depends upon three factors: First, the initial length of the brick which means that the longer its initial length, the more change that will occur in terms of the length of the brick, secondly, the temperature change (T) in that when the increase in temperature is significantly large there will be more increase in length, and thirdly, the properties of the substance itself in that an aluminum rod will twice increase in length than an iron rod of the same initial length (Schapery and Allan).

The difference in thermal expansion between iron and aluminum can be applied in an experiment and the results used to find out a "coefficient of linear expansion" to each of the substances. This coefficient is the factor of proportionality, after the consideration that alteration in dimensions is proportional to the alteration in the temperature and also to the initial dimension (Schapery and Allan). This can be represented in an equation l = al T. Both liquids and solids use this formula because they behave in a similar way.

Gases undergo more expansion than liquids and solids in relation to temperature increase and this expansion is not different in different gases. For these gases, in the presence of a constant pressure, the volume that is taken up by a gas is proportionate to its temperature. All this is represented by the equation VaT. For an ideal gas, the equation pV=nRt is used (Schapery and Allan). The constants rely on the amount of gas but not the type of gas. An application of this is the fact that a balloon floats because it is pumped with hot air than the air in the environment which has a higher density.

The first law of thermodynamics

This law states that the alteration in internal energy of a substance is equivalent to the work that is done on in addition to the heat transferred to it and all this is represented by the equation U =work + Q (Ostdiek and Bord). Work in this equation is used to mean the kind that transmits energy directly to the molecules and to atoms. An example of this type of work is the compression of a gas or lifting a particular object from the ground. Work can either be positive or negative in that if work is applied to a substance then it is positive but if the same substance is the one applying work on another, then the work is negative. An example is when air is blown into a balloon and it starts filling and expanding then the work is positive but when the balloon is left such that air comes out of it then the work is negative.

The temperature of a substance is dependent on the normal kinetic energy of the molecules and also of the atom. Matter behaves in such a way that for it to undergo an alteration in temperature, the atoms or molecules that constitute it have to acquire energy in the form of temperature increment or lose this energy in the form of temperature reduction (Cai, and Kim). The particles that constitute gases in this case only have kinetic energy and all of it is given to molecules and atoms to raise its temperature. This is a different case in solids and liquids in that in their case, molecules and atoms possess kinetic momentum and potential energy as they are held together and they vacillate. This, therefore, means that when energy is transferred to these substances, both their kinetic energy and their potential energy tend to get raised. This is the idea behind internal energy. The internal energy of a substance is the addition of the kinetic energies and the potential momentums of every molecule or atom in that particular substance. It is represented in Physics as U (Cai, and Kim). When the temperature of the substance increases, the internal energy also amplifies. If this results from the substance being exposed to a hotter substance then it is said that heat has been transmitted from the hotter to the cold substance. This heat is represented by the symbol Q and is measured in joules.

The second law of thermodynamics

This law state that no machine can be constructed to take away heat from a particular source and deliver mechanical work or mechanical energy without removing some of the heat to a low-temperature reservoir (Bekenstein). Fossil fuels cater for most of the energy being used in our society with some of these fuels being combusted directly for heating while most of them being put into use as energy sources for the machines that are classified as heat engines. A heat engine is a machine that converts heat energy into mechanical energy. It obtains heat from a source which includes burning fuels and transforms part of it into mechanical energy which is usable or into work and emits the remaining energy in the form of heat to reservoirs with lower temperatures. Heat engines include diesel engines and jet engines among others and most of these eject the unused heat into the environment via exhaust pipes or radiators or in some, the heated surface of the engine (Bekenstein).

This law is applied by the steam turbines that use very hot steam to rotate turbines which convert this mechanical energy to electrical energy and the remaining unused heated steam is directed to a low-temperature reservoir where it is cooled back to liquid water and taken back to the heating chamber. In Physical terms, energy in the form of heat is the input in this mechanism. Once the steam has reached the turbines, the heat is converted to mechanical energy and the remaining unused is rejected. The energy efficiency here is the functional output divided by the overall input then multiplied by 100% i.e. efficiency = (energy of work output/energy of work input) 100%. In case the result is 50%, this means that half of the energy is transformed to the useful form and the other half is wasted. The upper limit for this efficiency is known as Carnot efficiency which means there is no perfect heat engine (Bekenstein).

Specific heat capacity

This is the quantity of heat required to increase the temperature of the unit mass of a particular object or substance by a particular amount normally 1 (Ostdiek and Bord). This quantity of heat required is proportional to the rise in temperature. It has been proven that in order to increase the temperature 20 it would take twice as much heat as doing the same to 10. Therefore QaT is the equation for this scenario. The amount of heat required is also dependent on the mass of the matter to which the heat is transferred to. For a case where there is a given amplification in temperature, 2 Kg of water will need two times as much transfer of heat as 1 Kg. This requirement in heat transfer is also dependent on the substance as it takes more amount of heat to increase the temperature of water by 1 than it is required to increase the temperature of an iron with similar mass. As was the case with thermal expansion, a unique value can be allocated to different types of substances and this value is known as the specific heat capacity of the substance. The higher the specific heat capacity of a substance, the larger the quantity of heat transfer required to increase the temperature of the substance by a particular amount and is measured in joule/kg/ (Wakeham).

Phase transitions

A phase transition simply means the change in state of a substance from one type of matter to another (Ostdiek and Bord). This can occur in various ways: boi...