My Science School

          Atom bombs are a form of uncontrolled nuclear fission. When a large enough mass of uranium is put together, a fission reaction starts. The flood of neutrons emitted becomes so enormous that a vast amount of energy is released in a very short time, producing an atomic blast.

            Hydrogen bombs have an atomic bomb at their heart, but this core is surrounded by a layer of light material. Using the power released from the fission of the uranium or plutonium core, this layer of material causes a fusion reaction like the one in the core of the Sun. this nuclear fusion releases more heat energy than a fission explosion, as well as huge amounts of radioactivity.

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               Once nuclear fission takes place inside a nuclear reactor, the chain reaction has to be controlled, or moderated. The reactor’s core of uranium is surrounded with a substance that slows down and absorbs the escaping neutrons. The moderating material becomes heated. In a nuclear power station, steam generated by this heat is used to drive the turbines to produce electricity.

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               Nuclear energy is produced by changes in the nucleus of the atom of a radioactive element such as uranium or plutonium. This process is called nuclear fission. The nucleus is split by bombarding the atom with a neutron particle. Each time the uranium atom is split in this way, it releases energy. It also produces three more neutrons, which then go on to split other uranium atoms. This is called a chain reaction because, once started, it will continue the process of nuclear fission while releasing very large amounts of energy.

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               Radar works by sending out a beam of high- frequency radio waves, which are reflected back when they strike a solid object. The radio waves can also be reflected by clouds or other weather features. The reflected waves are collected and used to produce an image. Usually the radar beam is emitted from a rotating scanner, so a complete 360° image is produced. Radar is important in the navigation of ships, aircraft, and weather forecasting.

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               A silicon chip is a tiny wafer of silicon (a semiconductor) on which a complete electronic device can be produced. An image is produced photographically and etched onto the chip, but it differs from a printed circuit in some important ways. The chip is often microscopically small and contains huge amounts of ‘wiring’. More importantly, part of the process allows other devices to be produced in the manufacturing process, such as tiny resistors and capacitors. So a silicon chip, or integrated circuit, which measures just a few millimeters across, is a complete electronic device.

 

 

 

               Electronics depends on electricity. It uses changes in the voltage of an electrical current to convey messages or signals, usually in a coded form. The use of electronics is responsible for many activities that we now take for granted, such as radio and television, computers and calculators.

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               Any modern electrical device requires a huge number of connections to join together all the small components needed for it to work effectively. At one time these connections were made by wires that had to be soldered together. The wires have now been replaced by the printed circuit, which is effectively a picture of the wiring that works just as well.

               A thin sheet of copper is attached to a special board made of insulating material. An image of the electrical circuit is then printed photographically onto the copper sheet. Chemicals are used to dissolve most of the copper, leaving behind a thin film of metal bands, to which all the necessary components can be attached. This process can be carried out automatically.

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               Radio signals are transmitted using a carrier wave. A radio transmitter changes, or modulates, this radio wave in order to convey information. In AM radio the height of the carrier wave is altered according to the sound picked up by a microphone. In FM radio the frequency, or distance between the peaks in the radio wave, is changed. The radio receiver picks up these signals and amplifies and decodes them. If the signal is weak, AM radio sounds crackly. It is now being replaced by FM radio, which gives much clearer reception.

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               Radio waves form part of the electromagnetic spectrum. They are not part of the visible spectrum of light, and they have even longer wavelengths than infrared radiation. Radio waves with the longest wavelengths are bounced off a layer high up in the Earth’s atmosphere, called the ionosphere. In this way radio messages can be bounced for very long distances. Radio waves with shorter wavelengths penetrate the Earth’s atmosphere completely and can be used to communicate with spacecraft.

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               Many animals migrate for very long distances, but they arrive back at their birthplace in order to breed. This behaviour has puzzled scientists for many years, but they have now found that many of these creatures contain tiny particles of magnetite in special organs, allowing them to orientate themselves accurately.

               Magnetic navigation alone is not enough to account for the amazing ability of these animals to find their way over vast distances. It is thought that they also use other navigation aids, such as the position of the Sun, to help them.

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               Some experimental trains have been made to float a few centimeters above the ground by using a system of electromagnetic coils embedded in the track. Electromagnetic force can also be made to propel these trains. They have no wheels, so there is very little friction to waste energy. This magnetic propulsion system, which is completely silent, is called magnetic levitation.

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               Electromagnets only produce magnetism when an electrical current passes through them. They usually consist of a metal core made of iron or a similar material, around which are wrapped many coils of thin insulated wire. The metal core becomes magnetized when an electric current passes through the wire coil, but the effect disappears immediately the current is shut off. Very powerful electromagnets can be created by using many coils and strong electrical currents.

 

 

               Permanent magnets are usually made from mixtures of iron, cobalt and nickel, but others contain far more complicated mixtures of metals. Magnetite is a natural magnetic substance, which used to be called lodestone. It is a material that contains iron, and it was originally used to make the first primitive compasses.

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         One of the most important uses of magnets is electric motors, which are used to power machines ranging from small toys to enormous railway engines. Video and audio tape recorders also depend on magnetism. Their tapes contain tiny metal particles that are magnetized by the recording heads. When played back, another part of the head decodes the magnetic patterns. The hard drive and floppy disks in a computer work in a similar way.

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               The magnetized needle of a compass tries to align itself towards the Earth’s field of magnetic force. The magnetized needle balances on a pointed pin or floats on oil to allow it to rotate freely and to reduce friction. A compass needs to be used with care, because if it is near any object that can distort the Earth’s magnetic field it will give a false reading. A nearby object made of iron or steel, or any source of electrical power, will cause the compass needle to swing wildly.

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