First of all, letters and packets are collected in bags from pillar boxes, post offices and firms, in post office vans. They are then taken to the sorting office. Here the bags are emptied and the letters are separated from the packets. Following this step, the letters are put through machines so that the stamps can be cancelled. In this process the date and place of sorting are put over the stamps on each envelope. In the next stage, the sorting of the letters takes place, according to the county they are addressed to. This is done by placing them in the appropriate pigeon hole. Subsequently, the letters are taken from the pigeon holes and placed in baskets, which are then put onto a conveyor belt. While on this conveyor belt, the baskets are directed to the appropriate secondary sorting section by means of coding pegs. At the secondary sorting frames, the letters are put into towns in the county. Later, the letters are tied in bundles and a label is put on showing the towns they are addressed to. Finally, the letter bundles are placed in bags, which have the Post Office seal, Post Office Railway number and Destination Code number on them. These are then sent to the railway station.

MAKING A TRANSISTOR

In the first masking, the silicon base is coated with silicon dioxide. This doesn’t conduct electricity. It is then coated with a substance called photoresist. Then ultraviolet light is then shone through a patterned mask which hardens the photoresist. The parts which are not exposed to the light remain soft.

The next stage is the first etching. In this stage, a solvent is used to dissolve away the soft unexposed layer of photoresist. This exposes a part of the silicon dioxide. This exposed silicon dioxide is then chemically etched to reduce its thickness. The hardened photoresist is then dissolved to leave a ridge of dioxide.

Next is the second masking. Here layers of polysilicon, which conducts electricity, and photoresist are applied, and then a second masking operation is carried out.

Now comes the second etching. The unexposed photoresist is dissolved, and then an etching treatment removes the polysilicon and silicon dioxide beneath it. This reveals two strips of p-type silicon.

In the next stage, the hard photoresist is removed. The layers then undergo an operation called doping. This operation transforms the newly revealed strips of p-type silicon into n-type silicon.

The third masking stage and more etching follow. Now, layers of silicon dioxide and photoresist are added. Masking and etching creates holes through to the doped silicon and central polysilicon strip.

Finally, the photoresist is dissolved, and a final masking stage adds three strips of aluminium. These make electrical connections through the holes and complete the transistor.

In this transistor, known as an MOS type, a positive charge fed to the gate attracts electrons in the p-type silicon base. Current flows between the source and the drain, thereby switching the transistor on. A negative charge at the gate repels electrons and turns the current off.

Carbon is the basic element of organic chemistry and it undergoes a natural cycle in the environment. It exists naturally in the form of carbon dioxide in the atmosphere. From there it is absorbed by plants to build carbohydrates in the green leaves. When the plants burn, and animals breathe out, carbon dioxide passes back into the air. Also, in decaying plant and animal remains carbohydrates are broken down to release carbon dioxide into the atmosphere.

THE PHOTOCOPIER

A photocopier uses static electricity to produce almost instant copies of documents. At the heart of the machine is a metal drum. This is given a negative charge at the beginning of the copying cycle. The optical system then projects an image of the document on the drum. The electric charge disappears where light strikes the metal surface. So only dark parts of the image remain charged. Positively charged particles of toner powder are then applied to the drum. The charged parts of the drum attract the dark powder, which is then transferred to a piece of paper. A heater seals the powder to the paper, and a warm copy of the document emerges from the photocopier. A colour copier works in the same basic way, but scans the document with blue, green and red filters. It then transfers toner to the paper in three layers coloured yellow, magenta and cyan. The three colours overlap to give a full colour picture.

PAPERMAKING

Printing is of little use without paper.  Basically, a sheet of paper is a flattened mesh of interlocking plant fibres, mainly of wood and cotton. Making paper involves reducing a plant to its fibres, and then aligning the fibres and coating them with materials such as glues, pigments and mineral fillers.

Firstly, trees are felled and then they are transported to paper mills as logs.

Next, the bark has to be stripped off the logs, without damaging the wood.

Then, the wood is pulped. Pulping reduces the wood to a slurry of loose fibres in water. The logs are first sliced into chips and then they are treated with chemicals in a digester. These chemicals dissolve the lignin binding the wood fibres together. Alternatively, machines may grind the logs in water to produce pulp. The pulp is then bleached.

After that, the pulp goes to the mixer. The mixer is where materials are added to improve the quality of the paper. The additives include white fillers such as china clay, size for water-proofing, and coloured pigments. The mixer beats the fibres into a smooth pulp.

Then, liquid pulp is fed from the flowbox onto the mesh belt. The water drains through the holes in the mesh, and suction is used to accelerate the drainage. The dandy roll then presses the fibres together into a wet ribbon known as a web.

Belts move the web between the press rolls, which remove more water and compress the paper.

Finally, the damp web moves through the dryer, where it passes between hot cylinders and felt-covered belts that absorb water. It then passes through the calender stacks before being wound on reels or cut into sheets.

This is my Sony ICD MX 20 Digital Voice Recorder.
It is a digital recorder and player and I can use it to record myself or lectures and I can also connect it to my computer and download files on to it, which I can then listen to or connect to sound systems in classrooms to use in my teaching. It’s got excellent quality build – feels very firm and sturdy and it’s made of metal, not plastic. It’s definitely not going to break in the next couple of years. It also has excellent sound quality. And, particularly important, it has an expansion slot, so that I can put a memory card in and change the memory card record almost unlimited amounts.

As you can see it’s small rectangular in shape. Actually it is 37 mm wide, 100mm high and 24 mm deep. It is made of aluminium, which is very strong and light. It weighs just 96g, that’s including the batteries. On the front, you can see,  it has an LCD display – the display is about 25 mm square and it has a light – backlight – so that you can see it in the dark. On the front, there are also the controls and a small .28mm diameter loudspeaker. At the top it has a stereo microphone with a switch to make it more directional and long distant. On the left-hand side here it has earphone and microphone jack sockets. On the right hand side it has a Sony Memory Stick PRO Duo slot and a USB connector to allow you to transfer your recording to and from a PC. This means that I can change the memory card if I need to so, as I said, the amount I can record is unlimited. It uses a Sony Memory Stick PRO Duo card and at the moment, I have a 2GByte card in now. With the 2GByte card I can record up to 750 hours or, if I set it to best quality, as I usually do, 92 hours. That’s perfectly enough for what I need. You can see also that it has a volume control on the right hand side. At the bottom of the recorder, there is a battery container and a socket for an external power supply. It uses 2 standard type AAA batteries, and they last for 17 hours playing or 8 hours recording.

How does it work?
You can use it for recording or playing back. Before you use it, you need to set the recording mode. There are 4 possible recording modes from LP (Long Playing) mono setting to the best quality stereo setting. You also need to choose where you are going to store the recording. You can store it either on the internal memory – there’s 32MBytes of internal memory – or on the external memory stick. You can also choose one of the many folders that you can set up. Once you have set that, recording is very easy. You just press the record button and record. Press the pause button if you want a short break and press it again to restart. When you have finished, you press stop. It’s all very simple. The display gives you information such as where you are storing the recording, how much power your batteries contain and how much space there is on the memory stick. To play back, as before you first need to find the recording you want to listen to. So you have to navigate to the correct storage space and the correct folder. Then you find the file you want and press play. You can control the volume with the volume control on the right hand side and even, if you want, play the recording slowly. Of course, there are also many file management tasks you might like to do, such as deleting files, moving files to different folders and so on.

So it’s a very useful machine. It’s constructed very well; it’s made of metal, not plastic so it’s not going to break. It also has excellent sound quality. And, particularly important, it has an expansion slot, so that I can put a memory card in and record almost unlimited amounts.

NEWCOMEN’S STEAM – ATMOSPHERIC PUMP

I think you’ve all heard of James Watt, who is normally considered to be the person who invented the first modern steam engine. But actually, he got the idea for his steam engine from a primitive steam pump, which had been built by Thomas Newcomen in 1712.

In 1712, he’d built a pump, a steam-driven pump for pumping water out of the tin mines in south west England. Newcomen’s pump, as you can see, had two main parts, and these were positioned on either side of a wall. There was a pump mechanism on one side of the wall and a simple engine on the other side of the wall. These two parts were connected by a large pivoted beam. Attached to each end of the beam was a piston on a chain. The pump piston hung down inside a mine shaft, while the engine piston sat inside a cylinder, and this was mounted on top of a boiler. Above the cylinder was a tank containing cold water.

The system worked as follows. The weight of the pump piston pulled the beam down. Hot steam from the boiler then expanded and filled the cylinder. Then cold water was let into the cylinder. And the steam cooled and contracted. The pressure inside the cylinder was now lower than the atmospheric pressure outside. So air pressure on the top of the engine piston pushed it down. The beam was thus pulled down at the engine end and the piston came up the shaft, bringing water with it. The cycle was then repeated.