Category Science

Magnetism

 

 

What is magnetism?

Electrical currents are able to influence other electrical currents, and this force is called magnetism. Permanent magnets are materials in which this magnetic effect occurs because of the natural movement of electrons. Magnetism can also be caused by the flow of an electrical current through wires. The magnetic force of a magnet can repel (push) or attract (pull) another magnet or magnetic material.

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What is a magnetic field?

The area around a magnet where its magnetic force can be detected is called the magnetic field. You can see how this works if you lay a piece of paper over a magnet and sprinkle iron filings on it. The filings immediately arrange themselves in curved lines. You can see how these lines of magnetic force align themselves between the two poles, or ends, of the magnet.

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Radio and Electronics

What are silicon chips?

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.

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How do computers work?

A computer is a device for processing information very rapidly and accurately. It processes words, pictures, sounds and numbers, and some computers can make billions of calculations per second. Most computers are digital, which means that they convert all the data, or information, entering the computer into the digits 0 or 1.

The heart of a computer is a microprocessor, which contains millions of tiny electronic devices on a silicon chip. Other chips form the computer’s memory, where information is stored until needed. Computers vary from small hand-held devices to desktop computers. Large computers used in industry and for military purposes are called mainframe computers.

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How does radar work?

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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Radio and Electronics

What is a printed circuit?

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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What does ‘electronics’ mean?

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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Radio and Electronics

What are radio waves?

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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How does radio communication work?

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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The Changing Earth

How do we know that the climate has changed?

In more recent times, geologists and paleontologists have been able to make more accurate measurements of the age of ancient rocks. Trees produce a new ‘ring’ every year, and these can be measured and counted. The width of the ring shows how well the tree grew in any year, reflecting climatic conditions at that time. The rings of even partly fossilized trees buried in bogs can be measured, and these measurements provide accurate records of climate changes over the past 750,000 years. By measuring the radioactivity of once living material, scientists can make accurate measurements up to 40,000 years ago. 

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How was oil formed?

Most scientists think that oil was formed from the remains of tiny plants and animals that inhabited the seas millions of years ago. When these creatures died, their remains were buried in layers of rock. Substances in their bodies gradually altered to form oil. Other scientists disagree, and believe that oil formed from carbon-containing materials that were trapped inside the rock when the Earth was formed. Oil is found in rocks buried beneath the continents, and beneath the shallow parts of the oceans. More than half of the world’s known oil resources are in the Middle East. 

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The Changing Earth

 

 

Why did the world’s climate change?

The appearance of living things changed the Earth’s atmosphere, providing the conditions for climate change. The first living things were plant-like creatures. They used the Sun’s energy to change carbon dioxide and water into sugars, which they used for food, and oxygen, which they released into the atmosphere. Some of this oxygen turned into ozone, forming the layer that now protects us from the Sun’s ultraviolet radiation. 

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What effect did the Ice Age have on the world and its animals?

During an Ice Age, the enormous weight of the ice sheet presses the underlying rocks down, while those around the edges rise to form hills and valleys. The constant scouring action of glaciers shapes the Earth’s surface, wearing away complete mountain ranges. In an Ice Age, animals are forced to migrate to warmer areas. The ones that cannot adapt, for example mammoths and the woolly rhinoceroses, become extinct. The ice sheets on Greenland and in the Antarctic are the remains of the most recent Ice Age. 

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