Microwave Oven: The microwave oven is one of the great inventions of the 20th century - millions of homes in America have one. Microwave ovens are popular because they cook food incredibly quickly. They are also extremely efficient in their use of electricity because a microwave oven heats only the food - nothing else.
A microwave oven uses microwaves to heat food. Microwaves are radio waves. In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahartz (2.5 gigahartz). Radio waves in this frequency range have an interesting property: they are absorbed by water, fats and sugars. When they are absorbed they are converted directly into atomic motion - heat. Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.
You often hear that microwave ovens cook food "From the inside out." What does that mean? Here's an explanation to help make sense of microwave cooking.
Let's say you want to bake a cake in a conventional oven. Normally you would bake a cake at 350 degrees F or so, but let's say you accidentally set the oven at 600 degrees instead of 350. What is going to happen is that the outside of the cake will burn before the inside even gets warm. In a conventional oven, the heat has to migrate (by conduction) from the outside of the food toward the middle (See the HSW article entitled How a Thermos Works for a good explanation of conduction and other heat transfer processes). You also have dry, hot air on the outside of the food evaporating moisture. So the outside can be crispy and brown (e.g. - bread forms a crust) while the inside is moist.
In microwave cooking, the radio waves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. There is no "heat having to migrate toward the interior by conduction". There is heat everywhere all at once because the molecules are all excited together. There are limits of course. Radio waves penetrate unevenly in thick pieces of food (they don't make it all the way to the middle), and there are also "hot spots" caused by wave interference, but you get the idea. The whole heating process is different because you are "exciting atoms" rather than "conducting heat".
In a microwave oven, the air in the oven is at room temperture, so there is no way to form a crust. That is why foods like "Hot Pockets" come with a little cardboard/foil sleeve. You put the food in the sleeve and then microwave it. The sleeve reacts to microwave energy by becoming very hot. This exterior heat lets the crust become crispy as it would in a conventional oven.
This is a useful piece of technology as it heats your food in no time but it has its disadvantages as it doesn’t taste better than fresh food and some materials are not allowed such as metals it can cause bad damages to the microwave.
Washing Machine: these are used to make cleaning clothes easier as all you need is a washing powder and a bit of water. A washing machine has a round centre like a tub which rolls banging the clothes together with washing powder coming through and lots of water.
Operating a washing machine is pretty simple:
- There are a few things to decide before you start your load of clothes, such as how big the load is (small, medium, large, extra large), what temperature the water will be for the wash and rinse cycles (cold/cold, warm/cold, warm/warm, hot/cold), how the machine should agitate (delicate, knit, permanent press, heavy), and how long the cycles should last (number of minutes, based on how soiled your clothes are).
- After you fill the tub with clothes, the machine fills the tub with water, and then stirs the clothes around using an agitator.
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After some time agitating, the washer drains the water and then spins the clothes to remove most of the water. Then, it refills, and agitates the clothes some more to rinse out the soap. Then it drains and spins again.
These are also very useful but are very annoying at times such as when whites get mixed with other colours and when something gets stuck it messes up the wholes machine and this cost as well as water is pumped into it.
SCHOOL
Smart Card: this uses technology where you are electronically registered but these also help you gain points for coming to lessons and with enough points you can apply for gifts such as trips and pens. Every student is given a card which then is stuck into a machine then when the light switches from red to green to can take it out. A smart card – a type of chip card – is a plastic card embedded with a computer chip that stores and transacts data between users. This data is associated with either value or information or both and is stored and processed within the card’s chip, either a memory or microprocessor. The card data is transacted via a reader that is part of a computing system. Smart card-enhanced systems are in use today throughout several key applications, including healthcare, banking, entertainment and transportation. To various degrees, all applications can benefit from the added features and security that smart cards provide. Smart cards greatly improve the convenience and security of any transaction. They provide tamper-proof storage of user and account identity. Smart cards also provide vital components of system security for the exchange of data throughout virtually any type of network. They protect against a full range of security threats, from careless storage of user passwords to sophisticated system hacks. Multifunction cards can also serve as network system access and store value and other data.
This is quite a good idea but it really doesn’t work for me as waiting in the dinner line for the teacher the swipe is long and also putting money on your card can take long as people pushing in and wanting to get to the line. The idea of gifts are good but it takes to long for your to collect that much points
Printer: printer helps you to print out all sorts of layouts and sizes of documents these also print out in colour if cartridge are inserted which come separate colour or black. You can have different types of printers brought like laser printers :
A laser printer uses this phenomenon as a sort of "temporary glue." The core component of this system is the photoreceptor, typically a revolving drum or cylinder. This drum assembly is made out of highly photoconductive material that is discharged by light photons.
Initially, the drum is given a total positive charge by the charge corona wire, a wire with an electrical current running through it. (Some printers use a charged roller instead of a corona wire, but the principle is the same.) As the drum revolves, the printer shines a tiny laser beam across the surface to discharge certain points. In this way, the laser "draws" the letters and images to be printed as a pattern of electrical charges -- an electrostatic image. The system can also work with the charges reversed -- that is, a positive electrostatic image on a negative background.
Other then laser printers we at school also have injet printer not as good as laser but less expensive
An inkjet printer is any printer that places extremely small droplets of ink onto paper to create an image. If you ever look at a piece of paper that has come out of an inkjet printer, you know that:
- The dots are extremely small (usually between 50 and 60 microns in diameter), so small that they are tinier than the diameter of a human hair (70 microns)!
- The dots are positioned very precisely, with resolutions of up to 1440x720 dots per inch (dpi).
- The dots can have different colors combined together to create photo-quality images.
Printers are very useful as printing out pictures in good quality are neat and clear but due to less ink it can cause horrible outcomes as smudges and inks cost a lot. The technical faults can be annoying as if something isn’t right then it doesn’t work.
Photocopier: photocopiers is a bigger version of a scanner but easy and cans copier big documents such as A3 papers this is photocopied mostly in black but some can be photocopied in colour. The human-end of making a copy begins with a few basic steps:
- Open the copier lid
- Place the document to be photocopied face-down on the glass
- Select the options you want (number of pages, enlargements, lighter/darker)
- Press the Start button
What happens inside the copier at this point is amazing! At its heart, a copier works because of one basic physical principle: opposite charges attract.
As a kid, you probably played with static electricity and balloons. On a dry winter day, you can rub a balloon on your sweater and create enough static electricity in the balloon to create a noticeable force. For example, a balloon charged with static electricity will attract small bits of paper or particles of sugar very easily.
A copier uses a similar process.
- Inside a copier there is a special drum. The drum acts a lot like a balloon -- you can charge it with a form of static electricity.
- Inside the copier there is also a very fine black powder known as toner. The drum, charged with static electricity, can attract the toner particles.
There are three things about the drum and the toner that let a copier perform its magic:
- The drum can be selectively charged, so that only parts of it attract toner. In a copier, you make an "image" -- in static electricity -- on the surface of the drum. Where the original sheet of paper is black, you create static electricity on the drum. Where it is white you do not. What you want is for the white areas of the original sheet of paper to NOT attract toner. The way this selectivity is accomplished in a copier is with light -- this is why it's called a photocopier!
- Somehow the toner has to get onto the drum and then onto a sheet of paper. The drum selectively attracts toner. Then the sheet of paper gets charged with static electricity and it pulls the toner off the drum.
- The toner is heat sensitive, so the loose toner particles are attached (fused) to the paper with heat as soon as they come off the drum.
The drum, or belt, is made of photoconductive material. Here are the actual steps involved in making a photocopy:
- The surface of the drum is charged.
- An intense beam of light moves across the paper that you have placed on the copier's glass surface. Light is reflected from white areas of the paper and strikes the drum below.
- Wherever a photon of light hits, electrons are emitted from the photoconductive atoms in the drum and neutralize the positive charges above. Dark areas on the original (such as pictures or text) do not reflect light onto the drum, leaving regions of positive charges on the drum's surface.
- Negatively charged, dry, black pigment called toner is then spread over the surface of the drum, and the pigment particles adhere to the positive charges that remain.
- A positively charged sheet of paper then passes over the surface of the drum, attracting the beads of toner away from it.
- The paper is then heated and pressed to fuse the image formed by the toner to the paper's surface.
When the copier illuminates the sheet of paper on the glass surface of a copier, a pattern of the image is projected onto the positively charged photoreceptive drum below. Light reflected from blank areas on the page hits the drum and causes the charged particles coating the drum's surface to be neutralized. This leaves positive charges only where there are dark areas on the paper that did not reflect light. These positive charges attract negatively charged toner. The toner is then transferred and fused to a positively charged sheet of paper.
Inside a Photocopier
If you take a photocopier apart, you might be overwhelmed by how many different parts there are. However, the actual photocopying process relies on only a few, key pieces:
- Photoreceptor drum (or belt)
- Corona wires
- Lamp and lenses
- Toner
Photocopier are very useful at times because instead of you doing something again and again you can just copy it but sometimes it can become cut out by faults such as not pressing to hard on it.
