Lecture 1 Introduction to Energy and Matter, Electrical Conductivity PDF

Lecture 1 Introduction to Energy and Matter, Electrical conductivity In electrical engineering, we are often interested in communicating or transferring energy from one point to another. To do this requires an interconnection (electri...

Lecture 1 Introduction to Energy and Matter, Electrical conductivity In electrical engineering, we are often interested in communicating or transferring energy from one point to another. To do this requires an interconnection (electric circuit), and each component of the circuit is known as an element. An electric circuit is an interconnection of electrical elements. Energy Energy is essential for life. It is the ability to do work and allows us to live. There are many different forms of energy. Energy is the ability to do work or make objects move. For example, the energy stored in fuels like gasoline can be used to make a car move. The energy in gasoline is a form of energy called chemical energy. Law of Conservation of Energy The law of energy conservation is one of physics basic laws. The law of conservation of energy states that “In a closed system, i.e., a system that is isolated from its surroundings, the total energy of the system is conserved.” According to the law, the total energy in a system is conserved even though energy transformation occurs. Energy can be converted between the different energy forms, while overall energy is conserved. Energy can neither be created nor destroyed, it can only be converted from one form to another. The SI unit of energy is Joule. When we say casually that energy has been “consumed,” what we mean more precisely is that it has been degraded into less useful forms particularly into thermal energy that merely increases the ambient temperature. Different Types of Energy Although there are many forms of energy, it is broadly categorized into: 1. Kinetic Energy 2. Potential Energy Kinetic energy It is the energy associated with the object’s motion. Different types of kinetic energy: 1. Radiant energy Radiant energy, also known as electromagnetic radiation or energy, is found in electromagnetic waves such as visible light, ultraviolet rays, infrared rays, gamma rays, and radio waves. Sun rays are the main natural source of radiant energy, along with light from the 1 stars. Electromagnetic waves from the sun are the greatest source of natural radiant energy used to generate electricity through thermal collectors or photovoltaic panels, among other applications. 2. Thermal Energy Thermal energy (also called heat energy) is produced when a rise in temperature causes atoms and molecules to move faster and collide with each other. Thermal energy, or heat, is the energy that comes from the movement of atoms and molecules in a substance. Heat increases when these particles move faster. The energy that comes from the temperature of the heated substance is called thermal energy. An example, when you heat up the pizza in the oven, you raise the pizza’s temperature. The molecules that make up the pizza move more quickly when the pizza is piping hot. 3. Mechanical Energy Mechanical energy is the energy associated with the mechanical movement of objects. This type of energy can also be referred to as motion energy. 4. Electrical Energy The flow of negatively charged electrons around a circuit, results in electricity which we more commonly refer to as electrical energy. 5. Sound Energy Sound is produced when a force causes an object or substance to vibrate. The energy is transferred through the substance in a wave. It is energy moving through substances in longitudinal (compression/rarefaction) waves. Examples: voices, whistles, musical instruments and horns. Potential Energy Potential energy is the energy stored in an object or system of objects. Potential energy can transform into a more obvious form of kinetic energy. Different Types of Potential Energy 2 1) Gravitational energy It is energy stored in an object's height. The higher and heavier the object, the more gravitational energy is stored. When a person rides a bicycle down a steep hill and picks up speed, the gravitational energy is converted to motion energy. Another example, River water at the top of a waterfall. 2) Elastic Energy Elastic potential energy is stored as a result of applying a force to deform an elastic object. The energy is stored until the force is removed and the object springs back to its original shape, doing work in the process. The deformation could involve compressing, stretching or twisting the object. 3) Chemical energy The energy which is stored in the bonds of chemical compounds (molecules and atoms). It is released in the chemical reaction and mostly produces heat as a by-product, known as an exothermic reaction. Examples of stored chemical energy are biomass, batteries, natural gas, petroleum, and coal. Mostly, when the chemical energy is released from a substance, it is transformed into a new substance completely. For example, chemical energy is converted to thermal energy when people burn wood in a fireplace. Dry wood is the storage of chemical energy. When it burns, the chemical energy is liberated and converted into light energy and thermal energy. Please note that the wood transforms into ashes which is a new substance. 4) Nuclear energy It is energy stored in the nucleus of an atom—the energy that holds the nucleus together. Large amounts of energy can be released when the nuclei are combined or split apart. An example, uranium and plutonium store nuclear energy. Matter In a simple definition, Matter is anything that has mass and takes up space (volume). Matter is made up of small particles, known as atoms. Matter can be presented in different states, each of them has specific characteristics (solid, liquid and gas). Atoms Atoms are the basic building blocks of matter. They make up everything around us; Your desk, the board, your body, everything is made of atoms. Atoms are too small to see without powerful microscopes. 3  The atom is the smallest unit of matter that retains the identity of the substance. Each element has its own unique type of particle, known as its atom. Atoms of different elements are always different. The slightest change in an atom can make a tremendous difference in its behavior. You can live by breathing pure oxygen, but you can’t live off of pure nitrogen. Wood will burn furiously in an atmosphere of pure oxygen but will not even ignite in pure nitrogen. Yet both are gases at room temperature and pressure; both are colorless, both are odorless, and both are just about of equal weight. These substances are so different because oxygen has eight protons, while nitrogen has only seven. Protons, neutrons The part of an atom that gives an element its identity is the nucleus. It is made up of two kinds of particles, the proton and the neutron. Protons and neutrons have just about the same mass, but the proton has an electric charge while the neutron does not. The simplest element, hydrogen, has a nucleus made up of only one proton; there are usually no neutrons. This is the most common element in the universe. Sometimes a nucleus of hydrogen has a neutron or two along with the proton, but this does not occur very often. These “mutant” forms of hydrogen do, nonetheless, play significant roles in atomic physics. Electrons Surrounding the nucleus of an atom are particles having opposite electric charge from the protons. These are electrons. Physicists arbitrarily call the electrons’ charge negative, and the protons’ charge positive. An electron has exactly the same charge quantity as a proton, but with opposite polarity. The charge on a single electron or proton is the smallest possible electric charge. All charges, no matter how great, are multiples of this unit charge. The electrons are seen as so fast-moving, with patterns so complex, that it is not even possible to pinpoint them at any given instant of time. All that can be done is to say that an electron will just as likely be inside a certain sphere as outside. These spheres are known as electron shells. Their centers correspond to the position of the atomic nucleus. The farther away from the nucleus the shell, the more energy the electron has (Fig. 1-2). 1-2 Electrons move around the nucleus of an atom at defined levels corresponding to different energy states. This is a simplified drawing, depicting an electron gaining energy. Electrons can move rather easily from one atom to another in some materials. In other substances, it is difficult to get electrons to move. But in any case, it is far easier to move electrons 4 than it is to move protons. Electricity almost always results, in some way, from the motion of electrons in a material. Ions The ionization process begins with the entry of energy. Ionization, in chemistry and physics, any process by which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules (ions) through gaining or losing electrons. If an atom has more or less electrons than neutrons, that atom acquires an electrical charge. A shortage of electrons results in positive charge (cations); an excess of electrons gives a negative charge (Anions). The net charge on cation: Positive charge (as the number of electrons is less due to loss of electrons). The net charge on anion: Negative charge (as number of electrons is more due to gain of electrons). The element’s identity remains the same, no matter how great the excess or shortage of electrons. A charged atom is called an ion. When a substance contains many ions, the material is said to be ionized. The process of formation of ions is called ionization. Very high temperatures, electrical discharges, or nuclear radiation can cause ionization. Electric Conductivity We determine elements by their properties. One can easily distinguish between elements by the quality they possess. It has both physical and chemical properties. Their physical properties, such as malleability, phase, texture, color, polarity, solubility, etc. But as we know, another very important classification of elements is done based on their conductivity of electric charge, i.e. conductors and insulators. Electric conductivity is the ability of a material to pass an electric current through it. Every material has its own Electric conductivity. It is just the reciprocal of resistivity. In some materials, electrons move easily from atom to atom. In others, the electrons move with difficulty. And in some materials, it is almost impossible to get them to move. According to electrical conductivity, materials classified as the following: Conductors Conductors are the materials or substances which allow electricity to flow through them. They conduct electricity because they allow electrons to flow easily inside them from atom to atom. An electrical conductor is a substance in which the electrons are mobile. Conductors are materials with loosely attached valence electrons - electrons can drift freely between the atoms. Electrons in a conductor that are loosely bound to their atomic nuclei, and it do not move in a steady stream, that are constantly and randomly swapping positions from atom to atom right next to it. This happens to countless atoms all the time. 5  In a conductor, electrons are passed from atom to atom. An electrical conductor is defined as materials that allow electricity to flow through them easily. Conductors that let electricity flow freely are said to have a high conductance and a low resistance. Predicting the direction that electrons would move within a conducting material is a simple application of the two fundamental rules of charge interaction. Opposites attract and likes repel. Suppose that some method is used to impart a negative charge to an object at a given location. At the location where the charge is imparted, there is an excess of electrons. An object made of a conducting material will permit charge to be transferred across the entire surface of the object. If charge is transferred to the object at a given location, that charge is quickly distributed across the entire surface of the object. The distribution of charge is the result of electron movement. Since conductors allow for electrons to be transported from particle to particle, a charged object will always distribute its charge until the overall repulsive forces between excess electrons is minimized. Excess electrons migrate to distance themselves from their repulsive neighbors. In this sense, it is said that excess negative charge distributes itself throughout the surface of the conductor. If a charged conductor is touched to another object, the conductor can even transfer its charge to that object. The transfer of charge between objects occurs more readily if the second object is made of a conducting material. Conductors allow charge transfer through the free movement of electrons. The atomic structure of good conductors usually includes only one electron in their outer shell. It is called a valence electron. It is easily stripped from the atom, producing current flow. 6  The best conductor at room temperature is pure elemental silver. Copper and aluminum are also excellent electrical conductors. Iron, steel, and various other metals are fair to good conductors of electricity. In most electrical circuits and systems, copper or aluminum wire is used. Silver is impractical because of its high cost. Metals, humans, earth, and animals are all conductors. This is the reason we get electric shocks! Moreover, the human body is a good conductor. So, it provides a resistance-free path for the current to flow from wire to body. When we come in contact with a conductor, there occurs a flow of electrons from one body to another. This is the reason we experience shock. Shock is basically a mini feeling of current passing through the body. Some liquids are good electrical conductors. Mercury is one example. Salt water is a fair conductor. Gases are, in general, poor conductors of electricity. This is because the atoms or molecules are usually too far away to allow a free exchange of electrons. But if gas becomes ionized, it is a fair conductor of electricity. Some substances, such as carbon, conduct electricity fairly well but not really well. The conductivity can be changed by adding impurities like clay to a carbon paste, or by winding a thin wire into a coil. Electrical components made in this way are called resistors. They are important in electronic circuits because they allow for the control of current flow. The resistive element in carbon composition resistors is made from a mixture of finely powdered carbon and an insulating material, usually ceramic. The resistance is determined by the ratio of the fill material (the powdered ceramic) to the carbon. Resistors can be manufactured to have exact characteristics. Imagine telling each person in the line that they must pass a certain number of balls per minute. This is analogous to creating a resistor with a certain value of electrical resistance. Insulators Insulators are the materials or substances which resist or don’t allow the current to flow through them. Electrical insulators prevent electrical currents from flowing, except possibly in very small amounts. Insulators have structures where the electrons are bound to the atoms by ionic or covalent bonds - almost no current can flow. The atoms of the insulator have tightly bound electrons which cannot readily move. It has low conductance and high resistance which suppresses electrical current flow. Insulators are used in insulating electrical equipment for safety purpose. 7  Porcelain or glass can be used in electrical systems to keep short circuits from occurring. These devices, called insulators, come in various shapes and sizes for different applications. You can see them on high-voltage utility poles and towers. They hold the wire up without running the risk of a short circuit with the tower. Conductive objects are often mounted upon insulating objects. This arrangement of a conductor on top of an insulator prevents charge from being transferred from the conductive object to its surroundings. Most gases are good electrical insulators. Glass is the best insulator as it has the highest resistivity. A rubber is a common material used in making tires, fire-resistant clothes and slippers. This is because it is a very good insulator. Dry wood, paper, and plastics are other examples. Pure water is a good electrical insulator, although it conducts some current with even the slightest impurity. Metal oxides can be good insulators, even though the metal in pure form is a good conductor. An insulating material is sometimes called a dielectric. This term arises from the fact that it keeps electrical charges apart, preventing the flow of electrons that would equalize a charge difference between two places. Insulators are materials that hinder the free flow of electrons from one particle of the element to another. If we transfer some amount of charge to such an element at any point, the charge remains at the initial location and does not get distributed across the surface. Excellent insulating materials can be used to advantage in certain electrical components such as capacitors, where it is important that electrons not flow. Semiconductors Semiconductors are materials which have a conductivity between conductors (generally metals) and non-conductors or insulators (such as ceramics). Semiconductors can be compounds, such as gallium arsenide, or pure elements, such as germanium or silicon. In a semiconductor, the material is treated so that it has very special properties. The semiconductors include certain substances, such as silicon, selenium, or gallium, that have been “doped” by the addition of impurities like indium or antimony. Doping is the process of adding some impurity atoms in a pure or (intrinsic) semiconductor so as to increase the conductivity of a semiconductor. Semiconductors are used in diodes, transistors, and integrated circuits in almost limitless variety. These substances are what make it possible for you to have a computer in a briefcase. 8