UPSC 1998 Science and Technology Questions with Answers

Explanation

A fuse is a safety device designed to protect electrical circuits from overloads or short circuits. It works by having a thin wire or filament that melts when the current exceeds a certain level, breaking the circuit and preventing damage to electrical appliances. The fuse is specifically made with a low melting point to ensure it melts quickly in the event of excessive current flow, protecting the circuit from potential damage. Options (a), (b) and (d) are incorrect:

They are wired in series with the circuit not parallelbecause this setup ensures that the full current passing through the circuit flows through the fuse. This allows the fuse to effectively interrupt the circuit and halt the electrical flow in the event of an overcurrent. Fuses are not constructed from silver alloys as they are usually made from materials such as copper, zinc, or tin. They do not need high resistance rather, they should allow normal current flow until the current exceeds a safe limit. Direction: The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer this item using the code given below.

Explanation

Assertion (A) is true: The flow of electric current through a conductor causes energy dissipation in the form of heat due to the collisions between free electrons and the metal atoms. Reason (R) is true: As electrons travel through a metal as they collide with metal atoms causing the atoms to vibrate more and collide with each other which produces heat. The phenomenon is known as Joule heating. When current flows through the metal wire, the free electrons that carry the current interact with the metal atoms, transferring energy and causing the atoms to vibrate more, leading to a temperature increase due to Joule heating. The amount of heat generated depends on factors such as the wire’s resistance, the current, and the duration of the current flow. This effect is the foundation for devices like electric heaters. Thus Reason (R) explains Assertion (A)

Explanation

A is matched with 2: Dr. Raja Ramanna was a distinguished Indian physicist best known for his role in the development of India’s nuclear program, including the Pokhran-I nuclear test in 1974. B is matched with 5: Dr. Swaminathan is renowned for his contributions to the Green Revolution in India, which transformed the country into a self-sufficient food producer. His focus on developing high-yield and disease-resistant crop varieties, combined with sustainable agricultural practices, earned him global recognition in agricultural science. C is matched with 4: Prof. Udupi Ramachandra Rao was a visionary space scientist who led the design and launch of India’s first satellite, Aryabhata, in 1975. Also as the chairman of ISRO, he contributed significantly to advancing India’s space program. D is matched with 3: Prof. Meghnad Saha is celebrated for the Saha Ionization Equation, which explains the physical and chemical conditions in stars. He also made notable contributions to thermodynamics.

Explanation

Zirconium is an essential element for the construction of nuclear reactors due to its unique properties:

Low Neutron Absorption: Zirconium has a low neutron absorption cross-section, making it ideal for use in nuclear reactors as it does not interfere significantly with the nuclear chain reaction. High Corrosion Resistance: It is resistant to corrosion in the presence of coolant water, including high-temperature water, which is commonly used in nuclear reactors. Strength and Durability: Zirconium alloys are strong and durable, making them suitable for structural components like cladding for fuel rods. This combination of properties makes zirconium critical in the nuclear industry.

Explanation

A is matched with 4: Blue vitriol is the common name for copper sulphate, known for its bright blue color. B is matched with 3: Epsom salt is the common name for magnesium sulphate, often used in bath salts and as a laxative. C is matched with 1: Baking soda is sodium bicarbonate, used in cooking as a leavening agent. D is matched with 2: Caustic soda is the common name for sodium hydroxide (NaOH), a strong base used in industrial applications like soap making.

Explanation

A is matched with 2: Potassium bromide is widely used in the photographic industry. It acts as a restrainer in photographic developers and is used in the preparation of photographic emulsions. B is matched with 4: Potassium nitrate, also known as saltpeter, is a key ingredient in gunpowder due to its oxidizing properties. It releases oxygen during combustion, aiding in the rapid burning of other materials. C is matched with 1: Potassium sulphate is an important fertilizer that supplies potassium, a vital nutrient for plant growth. It is especially used in chloride-sensitive crops like potatoes, tobacco, and citrus fruits because it contains no chloride ions. D is matched with 3: Monopotassium tartrate is extensively used in baking. It helps stabilize egg whites, prevents sugar crystallization, and is a component of baking powder, contributing to the leavening process in cakes and bread.

Explanation

An amalgam is an alloy of mercury with another metal. While many metals can form amalgams, iron does not readily form one because it has a very low affinity for mercury under normal. On the other hand, metals like zinc, copper, and magnesium can form amalgams.

Explanation

Assertion A is true: Phenyl, a common household germicide, contains phenol derivatives that disrupt bacterial cell membranes and denature proteins, making it effective against germs. Reason R is true: Phenol, also called carbolic acid, is a well-known antiseptic and disinfectant due to its ability to kill bacteria, fungi, and viruses. This explains the germicidal property of phenyl. Thus, both Assertion (A) and Reason (R) are true, and R correctly explains A.

Explanation

Water pollution in rivers is primarily measured by the Dissolved Oxygen (DO) level, which indicates the amount of oxygen available for aquatic organisms. A low DO level signifies high pollution, as pollutants like organic waste decompose and consume oxygen, making the water uninhabitable for aquatic life. BOD (Biochemical Oxygen Demand) is the amount of oxygen required by microorganisms to decompose organic matter in water over a specific period (usually 5 days at 20°C). High BOD indicates organic pollution, such as from sewage or agricultural runoff, while low BOD signifies cleaner water. COD (Chemical Oxygen Demand) is the total amount of oxygen required to chemically oxidize both organic and inorganic matter in water. COD provides a broader measure of pollution than BOD, including oxygen demand from inorganic substances.

Explanation

Ergotism is historically known as "St. Anthony’s Fire" is directly linked to the consumption of grains (such as rye, barley, wheat, and oats) contaminated with the ergot fungus (Claviceps purpurea). The fungus infects the grains, producing sclerotia (ergot bodies) that contain toxic alkaloids. These alkaloids can cause two forms of ergotism:

Convulsive ergotism which is cracterized by seizures, hallucinations, and muscle spasms. Gangrenous ergotism which leads to restricted blood flow, causing tissue death and gangrene in extremities.