My Science School

          The simplest definition for the relay is that it is an electrically operated switch. The device is used where it is necessary to control a circuit by a low-power signal or where a number of circuits have to be controlled by one signal.

          Relays are controlled by electric current, magnetism or temperature. There are two types of relays - electromechanical and solid state. In the former, contacts are opened and closed using a magnetic force. With solid state relays, switching is done electronically.

          Electromechanical relays are general purpose relays. They are more common because they have lower cost, and can switch from AC or DC with equal ease.

     

Continue reading "Why did the relay make history? "

             Stephen Gray was an English astronomer who made significant contributions to science. These include his experiments with conduction, insulation, and electrostatic induction.

           One of his experiments was done using a glass tube. Gray observed that when the glass was rubbed with a dry hand or dry paper, it obtained electric charge. As a result, it attracted a feather to the glass, as well as the cork with which it was closed. The cork was in fact, used to keep the dust out when not in use.

          From the experiment, Gray concluded that the ‘attractive virtue’ passed from the tube to the cork.

         To clear his doubts, Gray proceeded with a similar experiment. This time, he attached an ivory ball to a piece of wood, and inserted the other end of the wood into the cork. Once it was done, he confirmed that attraction and repulsion passed to the ball, that too stronger than that on the cork.

         Gray observed that substances like silk do not conduct electricity. And that Earth was somehow responsible for conducting electric charge away from the body.

         For his electrical experiments, Stephen Gray received the first Copley Medal instituted by the Royal Society, in 1731. However most of his works went unacknowledged and he died as a poor man.

 

          A Leyden jar was the first device that could store electric charge. It was a glass jar with metal foil wrapped to its inside and outside surfaces. The jar would be partly filled with water, and had a wire running into it through the top part of the jar.

          There are two names involved with the invention of the jar. One is Ewald G. von Kleist, a German inventor who is said to have accidentally created it in 1745. The other is Pieter van Musschenbroek of Leyden, Holland, who ‘discovered’ the same thing in 1746. The latter invention spread through the world quickly, and thus Pieter gained more popularity for the invention.

          At first, it was thought that the electric charge was stored in the water inside the jar. In the 1700s, Benjamin Franklin studied much about this and proved that charge was stored in the glass. Hence, the later versions of Leyden jars had just metal foil wrapped inside and outside the glass.

          Technically, a Leyden jar is the prototype of the modern day capacitor which is used in almost all electronic equipment today.

 

                Benjamin Franklin invented the lightning rod in 1749. A lightning rod is a metal rod mounted on top of elevated structures like a building, tree, ship etc.

                It is electrically bonded with a wire with the ground or ‘earth’ through an electrode. Such an object protect a structure while lightning strikes. The idea behind it is that when lightning hits the building or tree, it will strike the rod.

              As a result, the electric power from lightning will be conducted to the ground through the wire, instead of passing through the building or tree. Thus, the structure can be saved from electrocution.

             Historians say that lightning rods were used in ancient times, and were particularly seen in the Sri Lankan kingdom of Anuradhapura, thousands of years ago. However, in the modern age, it was Benjamin Franklin who introduced the idea to the world. His aim was to create a tool that could save people from the dangers of the natural phenomenon. Through a series of experiments including the famous one using kite, he created the ‘Franklin rod’. 

            An electric motor is a device that converts electrical energy into mechanical energy. It works on the principle of electromagnetism.

            The first electrical motor is known to have been invented by a Scottish monk Andrew Gordon, in the 1740s. His motor was a simple electrostatic device.

            Almost a century later, British scientist Michael Faraday explained the conversion of electrical energy into mechanical energy by means of electromagnetism. The motor he created through the experiments was primitive, but it paved the way for later inventions. In 1822, British physicist Peter Barlow invented the first device to be powered by electromagnetism – known as Barlow’s Wheel.

            A decade later, British scientist William Sturgeon developed the first machine to be run on direct current. A few years after that, inventor Moritz Jacobi created the first real rotating electric motor that developed a remarkable mechanical output power. Frank Julian Sprague was the first to introduce a constant speed electric motor.

            All these have together contributed to the advancement of engineering technology in the world.

        Fuel cells are devices that generate electric current through chemical reactions. To put it better, a fuel cell uses chemical energy of hydrogen (or another fuel) to produce electricity in a clean and efficient manner. Its only products are electricity, heat, and water, and hence it is clean.

            There are a wide range of applications for which fuel cells can be used. This includes transportation, emergency power back up, material handling etc. compared to other technologies, fuel cells have many advantages. They are more efficient, and have lower emissions. That is, they do not emit dangerous substances like carbon dioxide or air pollutants, as their only products are water and heat. Yet another advantage is that fuel cells operate in a silent manner.

            The history of fuel cells began with the Welsh physicist Sir William Grove. In 1839, he demonstrated the first crude fuel cells. Although many people have tried to work on the concept of converting chemical energy into electric power, most of them were unsuccessful due to lack of resources.

            The first successful fuel cell was developed by the British engineer Francis Bacon in 1932, using hydrogen, oxygen, an alkaline electrolyte and nickel electrodes.