Category Chemistry

          It is a general belief that dust is very harmful to us. But this is only one side of the picture. Dust also is very useful to us. Before we go through the uses of dust, it is essential to know what dust is and how it is formed.

          Every solid substance is composed of very small particles. When these small particles of matter are scattered, they become dust particles. For example, if we break a brick or a stone into small pieces, it will turn into small particles of dust. There are different ways by which dust is formed. When solids break, dust is formed. Smoke generated by the burning of coal, wood, petrol etc, also produces dust. Dust particles also come from dead plant and animal matter, sea salt, desert, volcanic ash etc. These particles get mixed with air and are called dust particles. Air carries dust particles from one place to another. The particles of the earth’s surface also fly in the air in the form of dust.

          The biggest utility of dust particles is that they help in the formation of rains. The water-vapour in the clouds condenses on dust particles in the form of water-drops. These drops fall on to the earth as rains. The absence of dust particles can delay the rain. Likewise, mist, fog etc. are also formed due to the presence of dust particles in the atmosphere.

          The dust particles present in the atmosphere scatter sun-rays in all directions. Due to this scattering, there is not complete darkness for one to two hours even after the sun set. The appearance of red colour at the sunrise and the sunset is due to dust particles and water vapour. The beautiful rays of the sun seen in the twilight are also due to these dust particles. Thus we see that dust particles which are regarded as absolutely harmful by people are in reality very useful.

          It is a matter of common experience that ice floats on water. Howsoever large the size of ice may be it will not sink. Even icebergs which are huge masses of ice keep on floating in the sea. Do you know why ice floats on water?

          The law of floatation of bodies was given by the Greek scientist Archimedes. According to this law, whenever a body is placed in water, it is acted upon by two forces – the weight of the body acting downwards and the buoyant force of water acting upwards. If the weight of the body is equal to or less than the up thrust of water, the body floats on water. In other words, if the weight of the body is equal to or less than the weight of the water displaced by it, it will float on water. On the other hand, if the weight of the body is more than the weight of the water displaced, the body will sink in water. Hence a body floats when its weight is equal to the weight of the water displaced. A piece of wood floats on water because its weight is less than the weight of the water displaced by it. Since the weight of wood is nearly half of the weight of an equal volume of water, half of wood is under water, while the other half is above it. Similarly, the weight of cork is nearly one-fifth of the weight of the water displaced by it, so approximately one-fifth of cork is under water while the rest remains above water. You can understand the floatation of ice also on the basis of this law.

          In general, when a liquid changes to solid, it contracts because its molecules come closer to each other. As a result of this, the volume of the substance decreases or its density increases. Hence a substance becomes heavier in solid state than in the liquid state.

          But water is a peculiar liquid. When it becomes ice, instead of contracting, it expands. The volume of ice becomes more than that of the water. The effect of the increase in the volume of ice is that its density becomes nine-tenth of water, that is, ice becomes lighter than water. So we get about 10 litres of ice made out of 9 litres of water. And as you know, ‘litre’ is a measure of volume. That is why nearly nine-tenth of ice is submerged in water, while only one-tenth is above water. The ice under water (9/10 of the whole) displaces water whose weight equals that of the whole ice. This law of floatation is derived from Archimedes principle. This also explains how the maximum portion of the giant icebergs remains sub-merged in water while only a tip (1/10 part) is above water.

          Bursting of water pipes in cold regions is due to the volume of ice being greater than that of water. As soon as water freezes, the volume is increased which produces strong force due to which pipes burst? In Finland, this property is utilized in breaking rocks. Water is filled in empty spaces available between rocks. When water freezes, it expands and generates enough pressure to cause cracks in the rocks.

Polaroid photography is a photographic process in which the processing of the exposed film takes place inside the camera and the print is ready within a minute. It is based on a diffusion-transfer process, which makes it possible to produce a film negative and a positive print in one stage. Developed in 1947 by Edwin H. Land, the process makes use of a special film pack which also contains the printing paper and the processing chemicals. The chemical in the form of a jelly is contained in tiny capsules which burst as the film is moved after exposure. The name Polaroid comes from the name of the company with which Land was associated.

In the Polaroid process, after exposure the film passes through a pair of steel rollers in the camera which releases the developing chemicals. The chemicals convert the exposed silver salts on the negative layer into metallic silver. The unexposed silver salts from the film move to the positive emulsion layer on the paper by diffusion. There they are changed into silver, forming a positive image on the print. Colour film used in Polaroid camera has layers of coloured dyes in addition to negative and positive emulsions.

It is a clock which makes use of the piezoelectric properties of quartz. A quartz crystal has a natural frequency of vibration which depends upon its size and shape. If such a crystal is included in an electronic circuit which applies an oscillating electric field to its opposite faces at a frequency very close to its natural frequency, the entire circuit will resonate or vibrate at the natural frequency of the crystal. Moreover, this frequency of vibration will remain constant over considerable time. In a clock or a wrist-watch, this constant frequency of vibration is converted into electric pulses to drive a motor which in turn drives a gear train to operate the hands or alternatively, the pulses activate a digital display.

Quartz clocks are much more accurate than spring or pendulum clocks. They may accumulate an error of a few tens of seconds in one year. They are used in computers and microprocessors.

The theory of relativity was put forth by Albert Einstein in two parts. The first part called the special relativity theory was published in 1905. It stipulates that the velocity of light in vacuum is constant irrespective of the relative velocity of the source and the observer. As a consequence, the measurement of length is dependent upon the relative velocities of the measuring rod and the observer.

For example, to a stationary observer on a railway platform, a train moving with a speed approaching that of light appears shrunk lengthwise. At the same time, to a passenger looking through the window on the train, the railway platform and the observer appear shrunk. But, to both the observer on the platform and the train passenger the immediate surroundings appear normal.

The second part of this theory published in 1915 is called the general relativity theory. It states that the gravitational attraction between two objects is not due to an attractive force but because of a curvature produced in space-time continuum by mass. 

SETI is an acronym for Search for Extra Terrestrial Intelligence. The possibility that intelligent life might exist elsewhere in the universe arises from the fact that the universe is made up of billions and billions of galaxies each containing billions of stars. Even if small fractions of this large number of galaxies have planets with conditions suitable for the appearance of life, there could be several million planets with intelligent life capable of communicating with us using radio signals which are the simplest media of communication. Also radio waves are capable of travelling across astronomical distances carrying substantial information.

However, most of the stars are so far away from us that even at the speed of light it will take several tens or hundreds or even thousands of years for a radio signal from a planet of a distant star to reach the Earth. Another problem is, because of the large distance even the strongest signals would have become extremely weak by the time they reach us. But astronomers are hopeful. They are using very large antenna to collect radio signals however weak from alien civilizations. Scientists at the National Aeronautics and Space Administration (NASA) who launched SETI in 1993 are sending out powerful bursts of coded messages to outer space in the hope of getting a response. But it is too early to say if their efforts will bear fruit.