Hazards of ultraviolet radiation
Neeraj Gupta
WE know that the sun is a source of light and energy. The rays of light reach us in the form of electromagnetic radiations and are known as gamma rays, x-rays, ultraviolet rays, visible rays, infrared rays, microwaves, radiowaves.

Hazards of ultraviolet radiation
Neeraj Gupta

WE know that the sun is a source of light and energy. The rays of light reach us in the form of electromagnetic radiations and are known as gamma rays, x-rays, ultraviolet rays, visible rays, infrared rays, microwaves, radiowaves.

Or all the above rays the rays of light that have affected our plant and life on the earth in a dangerous way are ultraviolet rays.

Ultraviolet (uv) radiation is undetectable by the human eye, although when it falls on certain materials it may cause them to fluoresce — i.e., emit electromagnetic radiation of lower energy, such as visible light. Many insects, however, are able to see ultraviolet radiation. Ultraviolet radiation is produced by high-temperature surfaces, such as the sun, in a continuous spectrum and by atomic excitation in a gaseous discharge tube as a discrete spectrum of wavelengths. Most of the ultraviolet radiation in sunlight is absorbed by oxygen in the earth’s atmosphere, which forms the ozone layer of the lower stratosphere. Of the ultraviolet radiation that does reach the earth’s surface, almost 99 per cent is uva radiation. When the ozone layer becomes thin, more uvb radiation reaches the earth’s surface and may have hazardous effects on organisms.

We are aware of effects of sun exposure like sunburn, permanent skim damage, and damage of organic molecules by uv radiations.

Sun energy output is 386 billion megawatt! In spite of having small wavelength (billionth of metre), these uv radiations contain high amount of energy which can even penetrate our flesh and change structure of skin cells.

Uv radiations can be broken into three categories.

• Uva(315-400nm),
• Uvb(290-315nm,
• Uvc (100-290),

I often get questions from young people that are so basic that they seldom occur to educated engineers, doctors or run of the mill scientists. While I am thrilled that such questions are asked by our young persons I keep on postponing answers, partly because I do not know how but also because I am afraid of lapsing into jargon that might partly satisfy but may also be a clever way of hiding our ignorance. Finally I have decided to tackle, as an example, three questions of this type I have recently received. These are given below:

1. Why must bodies have mass?

2. Kindly explain the source of occurrence of the gravitational force?

3. We call a body charged when the number of protons and electrons is unequal. But we also say that electrons and protons are charged particles. Please tell me what is the cause of the charge present on electrons and protons?

Let us first remember what we know about each of these apparently arbitrary properties, phenomena and the laws governing them. First we consider mass and gravitation. We become aware of these soon after we begin picking up and throwing things. Quantification and names might come later but we soon find out that there is a relation between mass and weight. In fact, we think they are the same. That which is heavy is harder to move — in school science language it has more inertia. Usually sitting on earth surface we measure mass by weighing on a balance. We take gravitational force on the object as a measure of its inertial mass. It is practically found to be the same. The gravitational mass and the inertial mass being proportional to each other is a remarkable property of the universe and this might hide something rather deep. I am not asserting that we have found the reason for existence of mass, but we have established a non-trivial connection.

We find that all masses exert gravitational force. We have also found that this force is inversely proportional to the square of the distance between the masses. This is according to Newton's laws. General Relativity of Einstein has a different and more refined way of looking at it but in our humdrum world Newton suffices. But I am not in a position to give an a priori reason that demands that masses have a gravitational field. Similarly I would find it difficult to say on the basis of some other scientific principles that electrons and protons have negative and positive charges and electromagnetic phenomenon should exist.

I might point out that besides charge there are several other attributes in particles that have been discovered. These are discrete attributes like charge but different. This is not the occasion to go into details of particle physics, but only to say that these are not complexities but seem essential to understand and predict physical phenomena.

We can say, on the other hand, if none of these things — electric charge and other attributes — existed we would not have a universe of the kind we do. There would be no stars, no planets, no chemical elements and no life. Lot of what we know about our universe we have learnt through observation, experimentation and theory making. We have tried to reduce the number of ad hoc assumptions. We can understand physics, astronomy, chemistry and lot of biology in a consistent way. Tremendous success has been achieved in this regard. We have discovered and largely understood the nature of four different types of forces. No other forces have yet been encountered. We have been able to produce a unified way of describing three of these forces. We have understood gravity separately but have not been able to put it in a unified framework so far. This is because gravity and quantum mechanics have not been properly compounded. There is hope that this might happen in foreseeable future.

You would notice that we are trying to move beyond the enterprise of finding specific independent reasons for the workings of nature. The ambition is to find a theory that would explain everything! It is possible that in this quest a new vision might emerge through which everything would fall in place in a simple natural way and what has been so far learnt would be subsumed within that vision. Then the reason for everything - charge, mass, gravitation and a host of other attributes and forces would be that none of them is a useless appendix. The whole would not be possible without everything. But then you might ask: what was the reason for the whole? I might be facetious and counter: perhaps the whole had no choice but to exist!

I have gone through this type of discussion to point out that the questions asked by many of you are connected with the frontiers of science and philosophy. I am sure there would be a place for you to contribute if you pursue your curiosity with depth and diligence. We know an enormous amount but there is just as large a challenge ahead. That should give us some humility.