Day-664 | Daily MCQs | UPSC Prelims | SCIENCE AND TECHNOLOGY

Answer: B
Explanation
Statement 1 is correct: As opposed to electric motors, whose power comes from rotating motion, cryogenic engines are reaction engines. In order to work, they throw mass in one direction and rely on the reaction thrust in the opposite direction. A small amount of fuel goes to the turbine.
Statement 2 is incorrect: Cryogenic engines are liquid-propellant rocket engines which use a combustion reaction between liquid hydrogen and liquid oxygen (oxidizer) to generate thrust through complex cycles which are divided in different stages. This leads to higher fuel efficiency. Aviation Turbine Fuel is a high-grade and purer form of petrol which is used in jet engines. Cryogenic engines use liquid hydrogen and liquid oxygen.
Statement 3 is correct: Liquefaction of propellants increases their respective densities as compared to using very high pressure. Thus, more fuel can be carried on-board with a simplified tank design.
Advantages and disadvantages of cryogenic engines
The main advantages of cryogenic engines are:
● More environmental-friendly than other options
● Non-toxic and non-corrosive
● Able to reduce the cost of launch operations
● Efficient and high-specific impulse
● Safer than other options in terms of ground safety, they’re non-hypergolic
The disadvantages of this type of engine include:
● Liquid Hydrogen presents a low density
● Their cryogenic storage requires of complex equipment that must be carefully tailored by experts in cryogenic engineering
● Presents the need for devising an ignition system

Answer: B
Explanation
Statement 1 is correct: H5N1 virus is a type of avian influenza commonly known as the Bird Flu. H5N1 is endemic in some areas, most commonly Southeast and East Asia.
Statement 2 is incorrect: It is far more contagious than SARS Cov2 or the coronavirus. According to data from the World Health Organization (WHO), since 2003, 52 out of every 100 persons infected with the H5N1 virus have died, representing a fatality rate of more than 50%. In the meantime, the percentage of deaths from COVID-19 has decreased to 0.1% from 20% at the beginning of the pandemic.
Statement 3 is correct: There are several H5N1 vaccines for various of the avian H5N1 varieties. While vaccines can sometimes provide cross-protection against related flu strains, the best protection would be from a vaccine specifically produced for any future pandemic flu virus strain.

Answer: A
Explanation
Statement 1 is correct: Gamma-ray bursts (GRBs) are indeed the most energetic explosions in the universe, emitting extremely high-energy gamma-ray radiation. These bursts can release as much energy in a few seconds as the Sun will emit over its entire 10-billion-year lifetime.
Statement 2 is correct and is the correct explanation of statement 1: Gamma-ray bursts are thought to be associated with cataclysmic events such as the collapse of massive stars (known as supernovae) or the merger of neutron stars. During these events, immense amounts of energy are released, leading to the emission of gamma-ray radiation. Thus, statement 2 explains why gamma-ray bursts are the most energetic explosions in the universe.

Answer: A
Explanation
Example 1 is correct: Geothermal energy involves harnessing heat from the Earth’s interior to generate electricity. This process typically involves extracting hot water or steam from underground reservoirs and using it to drive turbines connected to generators. Heat transfer is involved in this process as heat moves from the Earth’s interior to the surface, where it can be utilized to generate power.
Example 2 is incorrect: Thermocouples are temperature sensors that work based on the principle of the Seebeck effect, where a voltage is generated when two dissimilar metals are joined at their ends. This voltage is proportional to the temperature difference between the two junctions of the metals. While the primary function of thermocouples is temperature measurement, heat transfer is not explicitly involved in their operation.
Example 3 is incorrect: Microwave ovens cook food by generating electromagnetic radiation in the microwave frequency range. This radiation interacts with water molecules in the food, causing them to vibrate and generate heat through friction. Thus, the heat transfer mechanism is not directly involved in microwave-based heating of food.

Answer: A
Explanation
Pair 1 is incorrect: A Trojan is any type of malware that disguises itself as legitimate software to deceive users into downloading it. Trojan Horses are named after the Ancient Greek story of the deceptive Trojan Horse that took down the city of Troy. Unlike viruses, Trojan Horses do not replicate themselves, but they can be just as destructive. Trojans also open a backdoor entry to the computer, giving commands to malicious actors or allowing malicious users/programs access to the system.
Pair 2 is incorrect: A worm is a standalone program that can self-replicate and spread independently. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without attaching to a host program and can run independently. A Worm takes advantage of file or information transport features on the system, which allows it to travel unaided.
Pair 3 is correct: A Computer Virus is a type of computer program that attaches itself to other programs or files when executed and writes its own code so it can spread from one program to another, leaving infections as it travels. Almost all Computer Viruses are attached to an executable file, which means the virus may exist on your computer, but it cannot infect the computer unless you click on, run or open the malicious program. It is important to note that a virus cannot be spread without social engineering and human action, such as clicking on a bad link or running an infected program to keep it going. People continue the spread of a computer virus, mostly unknowingly, by sharing infected files or sending emails with viruses as attachments in the email.