Normally, the light rays entering the eyes are bundled and refracted by the eye lens in such a way that they converge exactly on one point on the retina at the back of the eyeball. If the refractive power of the lens does not match the length of the eyeball, this ‘focus’ is shifted either in front of or behind the retina, and the vision becomes blurred.
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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!
Light penetrates into different transparent materials at different speeds. A beam of light coming from the air, for instance, changes its speed when it falls on the surface of the sea and enters water – it becomes slower. As a result, the light wave moves in a different direction; i.e., it gets deflected or refracted. This phenomenon of change in direction of the light wave due to change in its speed is called refraction.
The sun warms our planet, and the Earth releases a huge spectrum of radiation in the universe. Light is only a small part of this spectrum, namely, the visible portion of the spectrum – colours of the rainbow. We do not perceive other forms of radiation such as radio waves or microwaves. Light rays can travel through vacuum in the universe, but when they fall on the matter, they get refracted. This phenomenon of refraction is used in instruments such as lenses or glasses for people with weak eyesights.
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.
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.
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.
By current we mean the flow of negative charge, i.e., the flow of electrons. Metals have lots of electrons. Hence, current flows in them, and they are good conductors. Substances such as air and glass are bad conductors. We need a source of power, such as a battery, to bring the electrons in motion so that a bulb can start glowing. The battery has a positive (+) and a negative (-) terminal. There are a lot of electrons at the negative terminal and only a few at the positive one. The flow of electrons from the negative terminal to the positive terminal is the current. It is measured in amperes (A). The greater the difference in charges between the two terminals, the stronger will be the flow of the current. This difference is known as the electrical voltage. It is measured in volts (V).
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.