Science & Technology Previous Year Questions (PYQ) with Answers – Page 5

The transmitter of an optical fibre link must be small enough to couple light into a core a few micrometres across, must switch on and off millions or billions of times a second, and must emit in a narrow band of wavelengths; a light-emitting diode meets these conditions, and for…

At the receiving end of an optical fibre link the light pulses must be turned back into an electrical signal, and that is the work of a photodiode, a reverse-biased junction in which incident photons generate charge carriers and so a current proportional to the light falling on it; PIN…

A fibre-to-the-home connection runs from the operator's equipment to the subscriber's premises over a distance of kilometres, and for such runs single-mode fibre is used: its core is only a few micrometres wide, so light travels along one path, there is no spreading of the pulse from different paths arriving…

Beta is the current gain of a bipolar junction transistor in the common emitter configuration: a very small change in the base current produces a much larger change in the collector current, and the ratio of the two is beta, which commonly lies between about twenty and several hundred.

In a bipolar junction transistor the emitter injects carriers, the thin lightly doped base lets most of them through, and the collector gathers them, so the emitter current divides into a large collector current and a small base current; alpha is defined as the collector current divided by the emitter…

Swine flu is an influenza infection of the type first recognised in pigs, and the name itself records the animal in which the virus circulates before it passes to people; once it is in a human population it spreads from person to person by droplets.

Malaria is caused by the protozoan Plasmodium and carried by the female Anopheles mosquito, and kala azar, also called visceral leishmaniasis, is caused by the protozoan Leishmania donovani and carried by the sandfly.

Typhoid is caused by the bacterium Salmonella Typhi, which spreads through food and water contaminated with human waste, and it is prevented both by sanitation and by the typhoid conjugate vaccine.

The CANDU design, from which India's pressurised heavy water reactors descend, burns natural uranium, and natural uranium contains only about seven parts in a thousand of the fissile isotope uranium 235.

Shaurya is the land based version of the submarine launched K-15 Sagarika, and it is stored and fired from a sealed canister, which lets it be moved by road and launched at short notice.

NASA is the civilian space agency of the United States, established in 1958 after the launch of Sputnik, with its headquarters at Washington DC.

STUDSAT, short for Student Satellite, was the first pico satellite built in India. A pico satellite is one that weighs under about one kilogram, and STUDSAT weighed less than that.

Gaganyaan is the programme under which the Indian Space Research Organisation is preparing to send Indian astronauts into a low orbit around the Earth in a crew module of its own and bring them back safely.

Wing Commander Rakesh Sharma flew in April 1984 aboard the Soviet spacecraft Soyuz T-11 as part of a joint programme between the Soviet Union and India, and spent about eight days aboard the Salyut 7 space station.

Nirbhay is the long-range subsonic cruise missile designed and developed in India by the DRDO. Nirbhay was developed by DRDO's Aeronautical Development Establishment in Bengaluru.

Tejas is India's indigenous single-engine light combat aircraft built for the Indian Air Force. The Light Combat Aircraft programme was started in the 1980s to replace the ageing MiG-21 fleet.

PSLV mainly carries Earth observation satellites to low orbits, GSLV was built for communication satellites, and the other two statements describe the rockets wrongly.

3D printing, or additive manufacturing, builds objects layer by layer from a digital design, and it is used in all five fields listed.

Only blockchain is matched with its right field. Belle II is a particle physics experiment at the SuperKEKB electron-positron collider in Tsukuba, Japan; it studies B mesons to look for physics beyond the Standard Model, and Indian institutes such as TIFR take part in it.

India's GM mustard, Dhara Mustard Hybrid-11 (DMH-11), is built for hybrid seed production, not pest resistance. It carries the barnase and barstar genes taken from the soil bacterium Bacillus amyloliquefaciens.