In direct current, electrons flow only in one direction, but in alternating current, electrons keep switching their directions. Due to significant advantages of alternating current over direct current, electrical power distribution is nearly all in the form of alternating current today. For many appliances, such as lamps, direction of flow of electrons does not matter; for others, such as computers, the flow needs to be uniform. Hence, a ‘rectifier’ is connected to a computer, which converts the alternating current into direct current.
The light coming from the sun is mainly white light. In the white light, a lot of different colours are mixed. These colours are seen in a rainbow. A rainbow is formed in rainy seasons. Sunlight falling on the rain is deflected twice by the water droplets. When it enters the water droplets it is deflected first. The light is split into its component colours because the blue light with shorter wavelength bends more than the red light with longer wavelength. The split rays travel to the rear wall of the droplet, where they are refracted again when they come out. Thus, the rays form a colourful rainbow!
Fuses break the electric circuit when the current becomes very strong owing to any overload. As a result, the wires are never too hot, and a fire is prevented. In safety fuses, such as those used in cars or in screw-locking devices in homes, a thin wire inside the fuse melts when it gets heated by a very strong electric current. The fuse blows and must be replaced. In modern fuses, the circuit is broken with the help of an electromagnet, which ‘jumps out’ to break the circuit. When the fault has been fixed it is easily reset by pressing the switch.
Electricity travels from a place of high voltage to low voltage, just like water travels naturally from high elevation to low elevation. If the bird sits on a wire and also touches the ground, a path is created that allows electricity to travel through the body and to the place with no voltage. When electricity travels through the body of the bird in this fashion, electrocution takes place, and the bird dies. However, if the bird touches a single wire it does not get a shock because electric current passes through the wire instead of the bird.
European sockets provide electric current at 230 volts. Since, this voltage do not suffice to cover the large distance from the power plant to our homes, it is raised in the power plants with the help of transformers up to 380,000 volts. Locally, large substations or small ‘transformer houses’ transform the voltage to 230 volts. A transformer is like an electromagnet. The incoming high-voltage electric current generates a magnetic field in the coil. This permeates the neighbouring coil in the second electric circuit and generates a lower voltage: 230 volt.
Electricity plants convert the energy from the raw materials of the Earth into electrical current. This is done with the help of huge generators, which are driven by water, steam, or wind. Electricity is then distributed at a high voltage through cables laid in the ground or through overhead lines, on which often birds sit in swarms. Substations then produce electricity, which finally comes out of the sockets in our homes: 230 volts alternating current. However, many devices, such as computers, need direct current. Fuses protect us and our property from damages.
Leaving aside the volcanic areas, temperature in the upper layers of the Earth’s crust varies from 10 to 30°C. This weak geothermal energy can still be used by enriching it a little with heat pumps. In the naturally warm sources, the thermal sources, the heat energy of the Earth is used for medicinal purposes - as done by the ancient Romans.
This happens in a natural way in dung heaps, as also in compost plants, garbage dumps, and crops. In large biogas plants, the remains of the plants are decomposed by bacteria in an air-tight tank. The released gas is highly combustible because of its high methane content. The Earth has almost unlimited supply of plant remains, which makes biogas an important source of energy from renewable raw materials. It can be used as gas for heating or for generating electricity. It can also be liquefied easily and used as fuel for vehicles.
Glass mainly consists of lime, soda, and quartz sand. These three components are milled together finely, mixed with one another, and melted at about 1600°C in a furnace. When the molten glass is cooled to l000°C, it can be shaped into different objects. Depending on the intended use, the glass objects are shaped by pressing or drawing the molten glass. The used glass that we collect is also a valuable raw material, as it can be processed to make new glass objects.