Category Physics

          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’.