How do microwaves cook food?



Microwave ovens are quick. No one can argue with that. Cooking and reheating food which in normal ovens might take twenty or thirty minutes can be done in less than a tenth of that time in a microwave oven. With speed like that it’s no wonder they’ve become the latest kitchen craze.



When you think about it, not a lot has changed in cooking since the days when our primitive ancestors cooked up mammoth steaks in caves. They used fire to cook their food. And even the most up-to-date ovens still apply the same principle. They may not use fire, but the food is cooked by exposing it to outside heat.



Microwave cooking literally turns this inside out. Instead of cooking or heating food from the outside in, the food is cooked all the way through at the same time.



The electromagnetic waves that do the cooking or heating bombard the food at a fantastic rate. This stirs up the molecules in the food, creating heat right through it at the flick of a switch. The whole process is fantastically quick. Instead of waiting hungrily for something hot to eat, with a microwave oven it takes the same times to cook, eat and wash up a meal as it does to cook it in a conventional oven.



 



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Can you tell how computers work?



All computers work in basically the same way. They follow a set of instructions called a program that enables them to do calculations on information fed into them.



This process produces a result that is used in some way. The great advantage of computers over other machines is that the program can be changed, so that a computer can be given a wide variety of tasks to perform.



Computers consist of four main units – an input unit, a central processing unit is at the centre of operations and generally consists of a microchip located in the computer case. It controls the operations of all other units, which may be part of the computer or connected to it.



The input unit is used to feed information or data into the computer. It is usually a keyboard, but it may also be a light pen that interacts with a computer screen, or simpler devices such as a joystick, a mouse or a bar-code reader. The keyboard is also used to write programs.



The central processing unit first passes the information to the internal memory, where it is held temporarily. The program is also held in the memory, and the processing unit follows the program to produce the results. These go to the output unit, which is usually a video screen or printer, or they may be sent along telephone lines to other computers.



The computer also has an external memory unit such as disc drive that takes programs and data from the internal memory and records them for use at a later date.



 



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How computers are used in industry?



The electronic computer is used in many fields of activity and is extremely valuable in doing complicated work accurately and quickly. It has removed much of the drudgery from such routine tasks as telephone se wonderful machines work? We can see in the simple example of checking the stocks held by a warehouse.



In large scale industries it costs a great deal of money to keep a large number of goods in store. Nevertheless a company must always know how many goods it has at a given time in case it runs out of any item. So there must always be a reserve level below which stocks must not go. When that level is reached the company orders more goods to be delivered.



One way of keeping a check is to use a punched-card system. Each article which is delivered to the warehouse has its own card punched with required information which may relate to style, colour, price, size or other relevant details, and this is fed into computer.



When the article is sold and leaves the warehouse the computer is fed with this information too. At any time the computer can show exactly how many of those articles are in stock and if the stocks have to be replenished. The computer does this job with great speed and accuracy and can give an account of exactly how many articles of many different types are in stock.



The initial effect of computers is as an efficient means of performing complicated or routine tasks. In the long term, however, they will make new and different activities possible for instance, education and many occupations will be greatly affected as methods of storing and retrieving vast quantities of information are further developed.



 



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How radar works?



We have all at one time or another heard the echo of our own voice. An echo is caused by sound waves being bounced back from a solid obstacle, rather like a rubber ball bouncing off a wall. The same thing happens to radio waves which are sent out by a powerful transmitter. When the waves collide with a solid object they bounce back and can be picked up by a receiving set which is usually located at the same place as the transmitter. Since the speed of these waves is known we can tell how far away the obstacle is by calculating how long the waves take to cover the distance. This is how radar works.



The word ‘radar’ is an abbreviated form of the name ‘radio detection and ranging’. Radar is now used everywhere’ at airports, missile bases, space centers for following and tracking satellites and on ships and tracking satellites and on ships and aircraft for automatic navigation. A simple form of radar is used by police to detect speeding vehicles.



 



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Do you know how a rocket works?



You may have seen a certain type of lawn sprinkler which works by spinning round and round as the water squirts from it. The spinning movement is caused by the pressure of the water pushing against the movable arm of the sprinkler.



Sir Isaac Newton noticed something like this happening and it led him to discover an important law of nature. Newton’s law was that for every action in one direction there is an equal action in an opposite direction. In the case of the lawn sprinkler the water goes in and pushes in one direction and the sprinkler turns in the opposite direction.



The same law explains why a rifle recoils sharply when it is fired. The firing of the gun is known as the action and the recoil of the gun is the reaction.



The principle is what makes rockets speed through the air. Rockets are fuelled by very highly compressed gases. When these gases are violently released from the tail of the rocket the reaction they set up gives the rocket a mighty push in the direction opposite to the gas flow.



The greater the distance to be travelled, the greater must be the initial thrust. When Saturn V was launched, for example, its five engines consumed kerosene and liquid-oxygen at rate of 15 tons per second.



 



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