Compilation of  Q & A format of the book Science and Technology for Civil Services Examinations, Tata McGraw Hill Publication

1 . What is Photonics? How is it different from Electronics ?  What is the use of Photonics?
Photonics is the study of light, including its generation, propagation and interaction with matter, where light includes more than just visible wavelengths. In photonics, energy and information are carried by photons rather than electrons as in electronics. Photonics use the wave/particle nature of light to create high technology optical materials. They are expected to replace electronic components with optical components

2 . How does Photonics help computers?
It could lead to much higher memory capacities and a significant increase in data processing speed.

3 . In about a hundred words explain the applications of Photonics?
It can be used for bio-medical sensors and instrumentation and capillary electrophoresis, digital multimeters, power supplies, microwave systems, detection of cracks and corrosion under paint, carrier grade data networks, high-performance internet services and telecom networking products. It can be used for Industrial Process Control, Instrumentaion and Telecom. In Industrial Process Control, we can hace accelerated component life8testing equipment, Lab on a chip etc., In Telecon we can have high performance , intelligent and value added systems. In Instrumentation systems we can detect cracks and corrosion under paint. This work led to prototype detection devices for use on airplane wqings that are in the process of being brought to the market.

4 . Explain in a hundred words the medical uses of Photoncs.
Optical sensors that use photons as sensing elements are becoming increasingly important in the field of non-invasive diagnostics. Spectroscopic techniques are used for minimally invasive early detection of cervical, prostrate, oral and gastro-intestinal cancers. Photoplethysmography (PPG) is a non-invasive method for detecting the blood volume pulse. This information is analysed afrer interfacing with a computer. The bacteria and virus detection defence technology recognises the spectroscopic signatures of bacteria and viruses. Scientists are also developing a sophisticated photonic pill called the compact photonic explorer, that can perform remote diagnostics in the digestive tract and send information back to doctors.

5 . What is Laser?
Laser is a device that produces a very narrow, powerful beam of light. A laser beam can also be transmitted over long distances with no loss of power.

6 . What are the components of Lasers?
A typical laser contains 4 primary components-The active medium may be solid crystals such as ruby. They contain atoms whose electrons may be excited to an elevated energy level by an external energy source. The excitation mechanism or energy source pumps energy into the active medium .A high reflectance mirror at the ends of the optical cavity reflects essentially 100% of the laser light. There is also a mirror that reflects less than 100% of the laser light and transmits the remainder.

7 . Why is laser called coherent light?
A laser produces a thin, intense beam of light which is highly directional. Hence, it is also referred to as coherent light.

8 . What is class 1 laser? 412
A class 1 laser is considered safe for humans. This class includes all laser systems which cannot emit levels of optical radiation above the exposure limit for the eye under any conditions inherent in the design of the laser product.

9 . What is class 2 laser? When is it hazardous?
A class 2 laser system must emit a visible laser beam. Because of its brightness, it will be too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous as the upper radiant power limit of this type is less the MPE (Maximum Permissible Exposure) for an exposure of 0.25 second or less. Intentional extended viewing is however harmful.

10 . What is class 3 laser? Is it harmful to the skin? When does it cause harm?
A class 3 laser system can emit any wavelength, but it cannot produce a diffuse (not mirror-like) reflection hazard unless focussed or viewed for extended periods at close range. It is also not considered a serious skin hazard or fire hazard.

11 . How is laser useful in IT? 100 words
Lasers are particularly useful in recording, storing and transmitting information. The most common use is recording of music and motion pictures on compact disks. Bursts of laser light record such information on the disks in patterns of tiny pits. The laser beam’s tight focus allows much more information to be stored on a CD or DVD . Lasers can also read and play back information stored on these disks. In a CD or DVD, the laser beam reflects off the pattern of pits as the disk spins. Other devices in the player change the reflection into electrical signals and decode them as music.

12 . What is holography?
Laser beams can produce three-dimensional images in a photographic process called holography. Holography is a method for storing and displaying a three-dimensional image, usually on a photographic plate or any light-sensitive material. The exposed plate is called a hologram. Some credit cards contain holograms to prevent counterfeiting,

13 . How does a Laser printer work?
Laser printers use a scanning laser beam to produce copies of documents. Scanning involves movement of a laser beam across a surface. In a supermarket, what looks like a line of light is actually a rapidly moving laser beam scanning a bar code. A bar code consists of a pattern of lines and spaces that identifies a product.
14 . How are lasers useful in Medicine? 100 words
In medicine, the heating power of laser is often used in eye surgery. Highly focussed beams can close off broken blood vessels on the retina. It can also reattach a loose retina. Laser beams pass through the cornea but cause no pain or damage because the cornea is transparent and does not absorb light. Lasers are also used to treat skin disorders, remove birthmarks and shatter gallstones. Lasers can replace the scalpel, in some operations. They reduce bleeding and damage caused to nearby healthy tissues.

15. How are laser light shows created?
Laser light shows are created with scanning laser beams. The beams move so rapidly they produce what looks like a stationary picture. They can thus produce very colourful visual effects.

16 . How are lasers useful in ophthalmology?
The heating power of laser is often used in eye surgery. Highly focussed beams can close off broken blood vessels on the retina. It can also reattach a loose retina. Laser beams pass through the cornea but cause no pain or damage because the cornea is transparent and does not absorb light.

17 . What is a miniature hydrogen bomb explosion? 
In nuclear research, scientists use lasers to create controlled, miniature hydrogen bomb explosions. They focus many powerful laser beams onto a pellet of frozen forms of hydrogen. The intense beams compress the pellet and heat it to millions of degrees. This causes the nuclei to fuse and release energy.

18 . What is a pico second or femto second ?
A pico second is 10-12 seconds. A femto second is 10-15 seconds.

19 . What is line width and how  are lasers relevant here?
By careful design of the laser components, the purity of the laser light (measured as the line width) can be improved more than the purity any other light source. This makes the laser very useful for spectroscopy. It also makes techniques like Raman spectroscopy possible. It can also be used to make extremely sensitive detectors of various molecules.

20 . What is spectroscopy?
Spectroscopy is the study of interaction between matter and radiated energy.

21 . How are lasers helpful in measuring earthquakes and land surveys?
Laser beams directed over long distances can detect small movements of the ground. Such movements help geologists involved in earthquake warning systems. Laser devices used to measure shorter distances are called range finders. Surveyors use the devices to get information needed to make maps.

22. What are optical tweezers?
Optical tweezers involve grabbing, moving and generally manipulating, without any physical contact, micrometre-sized particles. This is based on the optical dipole or gradient force. They are based primarily on Newton’s laws and fundamental optics, and this has enabled an unprecedented insight into biological molecules such as the DNA.

23 . What exactly is Photonics?
Photonics deals with generating, controlling and detecting light and is based on a variety of materials. It also plays a major role in sensing.

24 . The human vision system is the ultimate interface between electronics and photonics. Explain
The eye and the brain work in perfect harmony. We sense others by photons, the quantised light waves that impinge on the retina. The optical information received by the retina is quickly converted into electrical impulses. These impulses travel through the optic nerve to the visual cortex of the brain.

25 .  What is EPIC?
Seamless union of electronics and photonics is the ultimate goal of the program for developing a single tiny chip of silicon that can not only manipulate and guide photons, but also convert photons into electrons and process the electrical signals. This program is called EPIC. It seeks to produce a single chip capable of emulating the eye and the brain.

26 . Describe the Photonics Development Programme in India 50 words. 417 -418
Its short term objective is to nurture photonic technologies, including those that are relevant to IT and optical communications such as optical fibres, optical amplifiers. The long term objective of the programme is to ensure that India has a presence as a technology developer in the broader application domains of photonics that include polymers used in nano-photonics and photonic crystal fibres, besides having a presence as an optical communication developer.

Chapter 31 Global Environmental issues

1 . Describe the Stratospheric  Ozone layer . 50 words
The stratospheric ozone layer is found in a broad band, generally extending from about 15 to 35 km above the earth. The profile and concentration of this layer depends on the dynamics of the winds, as well as sunlight and trace pollutants. The layer is surprisingly thin. But it is sufficient to filter out the bulk of the ultraviolet radiation that would otherwise reach the earth’s surface.

2 . What is the importance of this layer?   100 words
Life on earth evolved under the protection of an ozone layer thick enough to remove much of the UV-B radiation known to damage cellular DNA. YV-B rays are of high energy, which allows them to penetrate deeply into water, leaves and skin. It can harm metabolism of cells and damage genetic material. It could lead to increased incidence of skin cancer, eye damage and cataracts as well as inhibition of the immune system. Less stratospheric ozone also means less local heating. A weakened Ozone layer has also effects on climate. It could lea to decreased crop yields, damage to forst eco systems etc.,

3 .  What is stratospheric Ozone Destruction.? What are its consequences? 100 words
Ozone can be destroyed by chemicals that react with it directly, or by those that react with the oxygen atom temporarily freed when an ozone molecule splits. But, the only ozone destroyers of concern are those that can participate in a catalytic cycle, where one trace catalytic chemical can be responsible for destroying hundreds of thousands of ozone molecules. The detection of significant concentrations of CFCs in the lower atmosphere was coupled with the finding that photochemical and rain-out processes that usually remove most pollutants were not working for these compounds. They are extremely stable and have atmospheric lifetimes of 50 to several 100 years. Lesser stratospheric oxygen means less local heating, and that more ultraviolet light is transmitted to the earth’s surface causing skin cancer and damage to genetic material.

4. What is the Ozone Hole? What are its effects? 424
A massive continental-sized hole appeared over the continent of Antarctica in the spring of 1980. In the 1990s, this hole grew in size. The polar vortex was also responsible for the formation of the ozone hole. The winter stratospheric air over Antarctica is colder than the air elsewhere, which results in the formation of polar stratospheric clouds. This is because the strong confining winds of the polar vortex isolate this air from the warmer lower-altitude air. These cause greater chemical reactions and these chemicals are released during spring which in turn destroys the ozone. Lesser stratospheric oxygen means less local heating, and that more ultraviolet light is transmitted to the earth’s surface causing skin cancer and damage to genetic material.

5 . What is the Montreal  Protocol?424
As evidence emerged on the extent of the threat to the ozone layer, the international community agreed to control ozone-depleting substances and schedule a time-table for completely phasing them out. This agreement is known as the Montreal Protocol.

6 . What are the threats to the Ozone Layer apart from those caused by industry? 50 words  425
The solid rocket strap-on motors used in the most powerful launch systems, such as Ariane, produce copious amounts of HCL. A significant fraction of their exhaust gases is deposited in the stratosphere.. The plume from each launch causes a temporary mini ozone hole.

The chemicals that are replacing CFCs are HCFCs and HFCs. Though they have less chlorine in them as compared to CFCs, they are still ozone-depleting substances.

7 . What are the present threats to bio-diversity?
The present threats are overexploitation of resources such as hunting, introduction of foreign species including predators and diseases and environmental pollution. The most common threat is loss of habitat, due to deforestation, pollution of wetlands and ploughing up of Prairies.

8 . Describe the extent of Massive extinction of modern times.  426-427/50 words
Massive extinctions have occurred 5 times in the earth’s history, most notably 65 million years ago, when 15% of the species including dinosaurs were wiped out. There is strong evidence that we are in the opening phase of the 6th massive extinction. This extinction is unprecedented in both its breadth and speed. In the past 10,000 years, and especially in the last 500, the rate of extinction of species has increased to somewhere between 100 and 1000 times what it was before human history began.

9. What are the benefits of Biodiversity  to  humans? 100 words. 427-428
We derive many benefits from biodiversity. We get useful products from the wild. Nearly 25% of the drugs used today originally came from plants. One famous example is the anti-cancer drug taxol which was originally extracted from the Pacific yew. Other well-known discoveries from plants include quinine, penicillin and aspirin. It is also important to conserve genetic diversity within individual species. The breeding of new strains of pest-resistant crops and livestock is critically dependent on the supply of new genetic variability. This variability has been provided to scientists by wild relatives of domesticated plants and animals.

10 . Benefits of biodiversity conservation come from ecosystems and services. Comment 428
Soil nitrogen, a key element for agricultural productivity, depends on bacteria such as rhizobium, which live in the roots of leguminous plants. Micro-organisms also have the ability to carry out chemical reactions. A major breakthrough in genetic engineering- the polymerase chain reaction technique used to make copies of DNA- was possible because of the discovery of heat-stable enzymes in bacteria living in hot springs.

11. What is the value of Diverse Ecosystem?
Wetlands such as swamps, marshes and mangroves filter large quantities of pollutants from the water. They also serve as breeding grounds for fish, and are thus vital to the productivity of lakes and oceans. Forests and grasslands also absorb pollutants from industries and help purify the air. Plants too need a variety of micro-organisms to grow: bacteria and algae for nitrogen and fungi for phosphorus.

12 . What is the future of biodiversity? 100 words429
Steps have to be taken to stem the tide of the sixth extinction. An international treaty called CITES (convention on international trade in endangered species of flora and fauna) went into effect in 1975 to outlaw the trade of endangered animals and animal parts.

One of the key agreements adopted in Rio in 1992 was the Convention on Biological diversity. It established 3 main goals: the conservation of biological diversity, the sustainable use of its components, and the fair and equitable sharing of the benefits from the use of genetic resources. Preserving endangered eco-systems is an important way to protect the endangered species within them.

13 . What is Green House Effect? 430
Greenhouse effect is the warming of the lower atmosphere and surface of a planet. When the radiation from lands and seas strike certain gases, these substances absorb the heat and become heated. They are then cooled by sending out infrared rays of their own. Some of these rays come back to the earth’s surface, adding to the warming of the earth and the lower atmospheric levels.

14 . What is the relation between Green House Gases and Climate Change?  50 words
Since the 19th century, the amount of carbon-dioxide has increased by 25%, chiefly due to burning of fossil fuels. This and other greenhouse gases absorb the radiation from the earth’s surface, most of which is reflected back to the earth. This increases the temperature of the earth. This could lead to rising sea levels, greater severity of storms, and changing ocean and wind patterns. This affects agriculture, forestry and wildlife.