My Science School

           Benjamin Franklin conducted the famous kite experiment in Philadelphia, USA. The experiment was done to understand the ‘mystery’ behind lightning and electricity. Let us nee how it took place.

            The inspiration for the kite experiment came from Franklin’s conviction that lightning mid electricity had close similarities. To prove this, he went out with his son on a dark afternoon on June 10th, 1752. They attached a silk string to the kite, and tied an iron key to its end. Then, they tied a thin metal wire from the key, and inserted it into something called a Leyden jar, a container for storing electrical charge.

             Franklin’s idea was to fly the kite into the storm-clouds and conduct electricity down the string. Later, when lightning struck the kite, Franklin moved his hand towards the key. Guess what happened? A spark formed, and Franklin felt a shock. But luckily for Franklin, he was standing on an insulator, keeping dry under a roof, to avoid the danger of electric shock.

            However, with this dangerous experiment, it was proved that lightning was electrical in nature. 

            Benjamin Franklin firmly believed that electricity and lightning had close similarities.

            One of his inventions was the lightning rod, a simple rod attached to the top of a building. The rod was meant to protect houses from the destructive forces of lightning. As the electric charge from lightning strikes the rod, it would conduct the charge harmlessly into the ground, saving the house and its occupants.

           Franklin made a description of this invention in 1753. He is also credited to have coined terms like battery, conductor, electric shock etc.

           It is believed that Franklin began his experiments on electricity in 1746. Two years later, he created a multiple plate capacitor which he called an electrical battery. The capacitors were wired together sequentially to store more charge than one alone could. This helped to produce a bigger discharge of static electricity. For his contributions to the study of electricity, Benjamin Franklin received the Royal Society’s Copley Medal in 1753. 

          Lightning could be attractive to a few and scary to others, but it is definitely a phenomenon that stirs one’s curiosity! How many of us know that it is a powerful burst of electricity that happens very quickly during a thunderstorm?

         Technically, lightning is caused by an electric charge in the atmosphere. It is known to contain millions of volts of electricity. Lightning can occur inside, or between the clouds.

          Let’s see how lightning happens. Within the thunderclouds up in the sky, there are bits of frozen raindrops that rub against each other. This collision creates an electric charge. As it continues, the cloud fills up with electric charge. On top of the clouds the positively charged protons form, and at the bottom, negatively charged electrons. Since opposite charges attract, this results in a new charge building up. This charge concentrates on the ground under the cloud, mostly on things that stick up like mountains, tall trees, electric posts and even people. 

           A high voltage direct current (HVDC) is a transmission system that uses direct current for transmission of electric power in large quantities. Or, in other words, it is a technology used to transmit electricity over long distances. HVDC is also called a power super highway, or electrical super highway.

          We have seen that alternating current is preferred to direct current for various reasons, including financial. To address this, as well as other difficulties, HVDC can be used, as they are less expensive and suffer lower electrical losses.

          In this technology, electricity is transmitted through overhead transmission lines, or submarine cables. According to experts, the advantages of HVDC include lower investment cost, long distance water crossing, controllability, lower losses etc. It also causes lower environmental impact compared to AC.

            It was in 1882 that the first long distance transmission of electric power was demonstrated using direct current, in Germany. In the 1930s, the technology was further developed in Sweden and Germany. The modern form of HVDC also uses this technology.

            The Rio Madeira link in Brazil is the longest HVDC link in the world. The length of this link is 2385 kilometres. 

         All of us have heard of the term ‘voltage’ at some point. But how many of us know what exactly it is?

         Let’s try to understand with an example. If water has to pass through a hose, it needs some force from behind, doesn’t it? This force, in the context of electric power, is voltage.

          So technically, voltage is the name given to the electric force that causes electrons to flow from one atom to another. It is usually supplied by a battery or generator.

          One can observe voltage in the electrical appliances that we commonly use. We often see the brightness of light bulbs dimming. A reason for this could be a change in voltage. So, as the voltage increases, electric supply too increases. Devices called stabilizers are used in most of the domestic appliances like TV’s or fridges, to stabilize voltage.

          Voltage is measured in units of volts, and the equipment used for the purpose is called voltmeter. The term voltage was named after an Italian physicist Alessandro Volta.

 

          Direct current, as we know, is the flow of electric charge in just one direction. The history of electric power records that the first commercial transmission was made possible using direct current.

           This was perhaps because DC was the only option then. But as time passed, it proved to be insufficient. Because with direct current, voltage couldn’t be changed easily. What made it worse was that, different classes of loads, for instance, lighting, motors, and railway systems etc, required different voltages. So for this, there had to be different generators and circuits.

           However, in the course of time, alternating current took over and electric transmission became easier than before. We have seen that this type of current can reverse its direction, and serve better than DC. In 1884, the first long distance AC line was built in Italy, proving that AC was better for long distance transmission.

           As years passed, newer technologies were introduced. By the mid 1950s, an advanced type of direct current transmission was developed, and was named the high voltage direct current transmission. Today, it is the alternate and the most acceptable option for long distance, bulk transmission of electric power, especially between countries.

 

        Alternating current, as we saw, periodically reverses its direction, whereas direct current (DC) flows always in the same direction. The amount of current can change in a DC circuit, but their general direction remains the same.

         Perhaps the best and the simplest example of direct current is a battery. Take a look at one of them in your house. You can spot two terminals - +ve and -ve. If a wire is connected to these two terminals, it will cause a flow of electrons resulting in the production of electricity.

         Other than this, direct current is used as power supply for electronic systems and also for charging batteries. DC is thus used for many purposes, though for smaller and less complicated ones, unlike AC power. But direct current can be converted to alternating current through devices like an inverter or a motor-generator set.

         Direct current is produced by various sources such as solar cells, dynamos etc. It mainly flows in good conductors such as wire, but can also flow through semiconductors, insulators and even vacuum.

         Electric current in DC is measured in ampere and voltage in volts. 

        Electric current moves often like a water stream. The only difference here is that electric charges do not always move in the same direction. When they do, it is called Direct Current or DC.

        On the other hand, AC or Alternating Current, as the name suggests, occurs when charge carriers in a conductor, or semi conductor, reverse their direction of movement in a periodic manner.

        With AC, it is possible to run many types of electrical equipment like generators, motors, power distribution systems etc. and also kitchen appliances, TVs, electric lamps etc. Hence, for almost all high power applications, it is a global trend to use AC instead of DC because of its higher efficiency. Besides these advantages over DC, AC power is believed to be less expensive. One can also use high voltages with small currents to reduce losses, with AC power.

 

Continue reading "What is meant by AC? "

          You may have heard about conductors already. They are materials that allow electrons to flow freely from one particle to another. The capacity to transmit something such as heat or electricity is termed as conductivity. Depending on their conductivity, solids are classified as semiconductors, good conductors, and insulators.

           Objects that completely allow the passage of electricity are called good conductors. Pure silver is perhaps the best conductor we see around. Some liquids are good electric conductors too.

           Generally, gases are considered to be poor conductors. This is because their atoms are too far apart to allow free flow of electrons.

           Our body is said to be a good conductor of electricity. That is why we tend to receive electric shock from appliances or electric equipment.

           Insulators, on the other hand, do not permit the flow of electricity at all. Among the commonly seen insulators are glass, plastic, mica etc.

           Some materials like germanium and silicon belong to the category of semiconductors. This means they conduct electron flow under certain conditions. Otherwise, they act as poor conductors.

 

          The Ancient Greeks tried to study it some two thousand years ago. The man behind this attempt is known to be Thales of Miletus. He did research on the principle of static electricity.

          Around 585 BC, Thales conducted many experiments related to static electricity, a concept which was not conceived till then. He rubbed fur and clothes against amber to study more about the phenomenon.

          Amber is fossilized tree sap which is a plastic-like non-conducting material. Although he could not identify the secret force behind it, Thales was smart enough to see through attraction between unlikely objects. He could not have completed his study due to lack of resources and tools.

             The Greek contribution doesn’t end with this incomplete study. The very word ‘electricity’ has been derived from the Greek word ‘elektron’ meaning ‘amber’. 

       Static means steady, or unmoving. In physics, static electricity refers to that electricity which remains steady in a charged body. It is something that we come across in our daily life. An easy example could be the electricity produced when an object like a glass rod is rubbed against a piece of silk. Wonder how that happens? Let’s get to know.

       The fact that electric current is produced by the flow of electrons is something we already know by now. It is the friction between two objects that often result in this electron-transfer. This is how static charge is produced too.

         Take the example mentioned above. When a glass rod is rubbed against a piece of silk cloth, a few electrons from the rod moves to the cloth. As a result, the silk material turns negatively charged because of the excessive number of electrons. At the same time, having lost electrons, the rod becomes positively charged. As the process of rubbing continues, charge accumulated on the glass rod increases, and the pool of electrons that is formed on the other end creates what is known as ‘static electricity’. 

         Usually we talk about electricity as current. But are the two same? No!

         Let’s see why. As we have seen earlier, electricity is a form of energy. But electric current, on the other hand, is the movement of electric charge.

         Let’s put it better. It is the flow of charged particles through a medium such as a wire. Similar to water molecules moving down a river, charged particles move down a ‘conductor’ giving electric current. Conductor means anything that allows the movement of electric current for example, metals, and some liquids.

         Electric current is measured using a device called an ammeter. The conventional symbol for current is I.

        The intensity of electric current is measured in terms of ‘ampere’, named after the French scientist Andre-Marie Ampere, one of the founders of classical electromagnetism. 

          Electrons, as we know, are negatively charged subatomic particles. They are very important because of their role in various physical phenomena such as electricity, magnetism, etc.

           The history of electrons dates back to 1838, when Richard Laming put forth the concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Years later, in 1891, Irish physicist George Johnstone Stoney named this charge ‘electron’. Six years after that, British physicist J.J. Thomson identified the particle. The word ‘electron’ is thought to be a combination of the words ‘electric’ and ‘ion’.

           Inside the atom, electrons are in constant motion, revolving around the nucleus.

           They possess a certain amount of energy to maintain distance from the oppositely charged protons inside the nucleus.

 

         A proton is the positively charged subatomic particle located inside a nucleus.

         Protons are important because it is their number that determines the element (of which the atom is part) and its chemical properties.

         To put it simply, the number of protons in an atom, or the atomic number, defines the type of an atom. Thus an oxygen atom differs from a helium atom on the basis of its atomic number. That number is denoted by the letter ‘Z’.

         The word ‘proton’ was derived from a Greek word meaning ‘first’. It was named by Ernest Rutherford in 1920. One or more protons are present in every nucleus. Together, protons and neutrons form what is known as nucleons.

         Further, protons are made up of invisible particles called ‘quarks’. There is a strong nuclear force that binds these quarks with each other. It is also the same force that primarily contributes to the mass of the proton, rather than the quarks themselves.

 

        Electric charge is the physical property of matter.

        There are two types of electric charges: positive and negative. Like charges (positive and positive, for example) repel, and unlike charges (positive and negative) attract. The most common charge carriers are the positively charged proton and the negatively charged electron. An object is negatively charged if it has an excess of electrons.

        As per the International System of Units (SI), the unit of electric charge is coulomb, which is equivalent to about 6.242x1018 e. In electrical engineering, the unit is seen as ampere-hour (Ah), and, in chemistry, it is common to use the elementary charge (e) as a unit.

        By convention, the charge of an electron is -1, while that of a proton is +1. The quantity of electric charge can be measured with an electrometer.

        The study of charged particles, and how their interactions are mediated by photons, is called quantum electrodynamics.