Category Physics

How does a currency counting machine work?

          There are thousands of banks in the world where currency notes are counted and packed in the denominations of hundreds. Job of counting and packing is done by a large number of people. The job of counting the currency notes is quite boring. Scientists have developed a machine which automatically counts and packs the currency notes. This machine is a wonder of electronics.

          Working principles of a currency counting machine is shown schematically in the figure. The bundle of notes to be counted is placed on platform P-1. These notes are pushed in the forward direction by a feeding roller R-1. These notes are counted by a sensor S-1. Thereafter the notes pass through the rollers R-2 and R-3 and channel C-1. Through the channel the notes reach the sensor S-2. In case of any error in counting, S-2 will shut the motor automatically and display the mistake. After sensor S-2, rollers R-4 and R-5 pick up the notes and throw them into the slots of the centrifuge roller. These notes are released as they reach the platform P-2 and start stacking upon it. This platform is equipped with another sensor S-3 which indicates whether P-2 is empty or loaded.

           It is a microprocessor based machine and hence its reliability is very high. These machines can not only count currency notes but also the coins. These are portable machines and can be installed anywhere. Nowadays these machines are being used by many banks.

What is a Silicon Chip?

          The microchip or silicon chip has completely changed the colour of the electronic world by providing a new direction to it. It has led to the invention of electronic calculators, personal computers, digital watches, microwave ovens etc.

          The silicon chips are tiny crystals of silicon which contain large number of electronic components. Silicon is the most abundant element on earth as the crust of the earth is largely made of silicon. But silicon is not found in a free state as it is always combined with one or more additional elements. In one sq. cm. chip, about one million electronic components can be squeezed. The size of a chip is smaller than our finger tips. They can be made to carry very small electrical circuits, called microcircuits. These are used in transistor radios, digital watches, calculators and computers. They can be used in small electronic devices as the chips are very small.

          But how is silicon chips made? Silicon chips are made from a single crystal of silicon. Thin wafers of about 0.5 mm thick are sliced from a single crystal. One side of each wafer is first polished and then oxidized in a furnace: The disc is covered with a layer of photo resist material and then exposed to ultraviolet light through the clear sections of a mask. A light sensitive coating is developed and the exposed areas are dissolved away by the solvent. Unexposed areas are not affected so a pattern remains identical to the mask. The exposed areas are etched in hydrofluoric acid. Another solvent removes the resist. In a furnace, the wafer is exposed to chemicals which penetrate the silicon through the oxide gap to make transistors. The process is repeated several times. The wafer is coated with aluminium and a final layer of metals connects the components together. After careful inspection, chips are selected and released for use.

          Nowadays microchips are being used in electronic sewing machines, washing machines, word processors, and so on. 

What is a space suit?

          We know that the atmosphere at the Earth’s surface produces a pressure equal to the weight of a large automobile on each square metre. We do not notice this since it is equal both inside and outside our bodies. But if the air inside a metal pot is, for instance, forced out by boiling water inside it, the pot collapses under this pressure.

          Similarly, an unprotected astronaut in a space flight would not only die by swelling up, but his blood would also start to boil. The temperature at which a liquid boils depends on the atmospheric pressure. At a height of 9 km, water boils at 74°C; and above 19 kms, blood boils below body temperature. At zero pressure, the astronaut’s blood would instantly turn to deadly foam.

          Therefore, keeping these aspects in view, a space suit is specially designed so as to protect an astronaut from the dangers of space during space flights. Space dangers include extreme temperature, hazardous radiations, fast moving particles, vacuum etc.

          Space suit clothing is made of several layers each of which has a specific purpose. One of the inner layers controls the temperature. With the help of this Manned Manoeuvring Unit (MMU), an astronaut can leave the space craft and fly independently. It has the provision for oxygen gas. Each suit has got a primary life support system. It holds enough water and oxygen to enable the astronaut to carry out space walks for several hours. The space suit has the liquid cooling and ventilation system. In fact each suit is made from a number of different pieces. Each piece is made by selecting the sizes. Individual astronaut is given a suit from these so as to fit him.

          One very surprising thing about MMU is its weight. On earth it weighs about 158 kgs but when used in space it makes the astronaut very mobile. This is because of the weightlessness conditions in the space.

          A space suit therefore is a life-saving device for an astronaut.

 

How is the distance of stars from the earth measured?

          The stars which we see shining at night look very attractive and bright. Some stars look brighter than others. This is so because their sizes and distances from the earth are different. These stars are billions of miles away from our earth and shine with their own light. Do you know how the distance of stars form of earth is measured?

          Scientists have evolved a simple technique to measure the distance of the nearby stars. Suppose we want to measure the distance of a particular star ‘C’. We take its photograph from a place ‘A’ on the earth. After six months, the earth is at the position ‘B’, since it is revolving round the sun. We now take another photograph of the same star from the position ‘B’. A comparison of the two photographs will show that ‘AB’ is the diameter of the earth’s orbit round the sun and is equal to 186 million miles. Now the angle ‘ACB’ is measured. With the help of these two figures, the distance of the star ‘C’ is measured. This is known as the method of triangulation.

          Using this technique, the distance of many stars has been measured. The distance of Alpha Centauri from earth has been found to be about 4.35 light years. The distance of the Sirius has been determined to be 8.48 light years. However, this technique is not suitable for measuring the distance of very distant stars. The distance of such stars is determined on the basis of their brightness or colour. The most widely used system for measuring the distance of stars is the two-dimensional classification method developed by J.M.Johnson and W.W. Morgan. This system is based upon photoelectric measurement in three wavelength bands in ultra-violet, blue and yellow (or visual) regions of spectrum. This method is known as UBV system. Scientists have succeeded in measuring the distance of stars as far away as 8 million light years from the earth.

 

How can we test the purity of milk?

             The instrument used to assess the purity of milk is called a ‘lactometer’. It is a cylindrical vessel made by blowing a glass tube. One end of the glass tube is blown in the form of a bulb and filled with mercury. The other end is blown in the form of a thin tube and sealed. For calibration it is dipped in pure milk. The point up to which it sinks in the pure milk is marked ‘M’. After that it is put in water and is marked ‘W’ at the point up to which it sinks in water. It sinks less in milk than in water because milk is denser than water. The portion between ‘M’ and ‘W’ is divided into three parts and marked as 3, 2 and 1 to indicate the level of purity.

              Whenever we want to test the purity of milk, the instrument is put in milk. If it sinks up to the mark ‘M’, the milk is pure. If the milk is not pure, but mixed with water, it would sink to a mark higher than ‘M’. When the instrument stands at the mark 3, the milk is 75% pure. At the mark 2, the purity is only 50%. Mark 1 indicates a purity of 25%.

            Even though lactometer is commonly used to measure the purity of milk, yet, it is not a very reliable instrument. It has been observed that in the case of skimmed milk (denser than pure milk) that the lactometer fails to give the correct assessment of the purity, if the density of the skimmed milk is made equal to that of the pure milk by adding water in an appropriate proportion.

What is Paging Service?

            The 21st century would take people to a world of mechanical solidarity with courtesy from services like paging service, cellular telephone and Internet etc. Having acquainted ourselves with services like cellular telephone and Internet earlier, now let us discuss what paging service is all about.

            Paging is a one-way wireless communication providing instant access to the person being paged. One-way communication means that the subscriber only receives the message and can not communicate back instantly. The subscribers receive messages from anyone with access to a telephone. The modus operandi is as follow: The paging network of a particular region is co-ordinated by a ‘pagers exchange’ or network operator. Subscribers have a paging number assigned exclusively to them by the concerned network operator. The person who wants to send a message to a subscriber rings up the operator and leaves the message with him along with the subscriber’s paging number. Then the operator relays the message to the subscriber either directly or through any other regional operator. The message is then received by a small palm-size device called ‘pager’ kept by the subscriber with himself. An alarm sound from the device alerts the subscriber who then reads the message, flashed on the screen of the device. Some pagers also vibrate to alert the subscriber of an incoming message. The main advantage which a pager provides is that the subscriber receives the message wherever he may be since he carries the wireless device (pager) always with him.

            In India, as of now, the government has issued licenses to private operators to provide paging service to interested people and the number of subscribers is growing fast. As per current estimates, the running cost of a pager for monthly service would be around a couple of hundred rupees and a pager, at the moment, costs about a few thousand rupees. It is now the cheapest and most reliable one-way communication system available in the market today. Although its primary use is to get a message across fast, it has other potential uses such as getting across share market information by the business circles or to have latest cricket scores, for instance. The only demerit is that it provides only one-way communication as the receiver can not communicate back to the caller.