Science and Technology: UPSC Previous Year Questions (Prelims)

Explanation

Capillarity, also known as capillary action, is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. Capillarity is crucial in various natural and artificial processes, where the balance of forces drives the liquid into confined spaces.

Option (a) is correct: The tiny pores in the blotting paper act as capillaries and draw the ink through them.

Option (b) is incorrect: This is primarily due to hydrostatic pressure and not capillary action. Water moves through soil and rock layers due to pressure gradients rather than the effects of surface tension.

Option (c) is correct: This is due to capillarity. The fine fibers in the cloth act as capillaries, drawing water into them.

Option (d) is correct: Capillary action, along with transpiration pull and root pressure, helps move water through the tiny xylem vessels in plants.

Explanation

Cryogenics is a branch of physics that focuses on the production and study of materials and phenomena at extremely low temperatures, typically below -150 degree celsius. At these temperatures, materials exhibit unique physical properties that are not observed under normal conditions.

Option (a) is correct: Cryogenics has three major applications:

Space Travel: Used in rocket propulsion with cryogenic fuels like liquid hydrogen (LH2) and liquid oxygen (LOX) for efficient and high-energy space missions. Surgery: Applied in cryosurgery to destroy diseased tissue using extremely low temperatures, benefiting fields like dermatology and oncology. Magnetic Levitation: Enables superconducting magnets in Maglev trains and devices by cooling materials to achieve zero electrical resistance, allowing frictionless transportation.

Explanation

When light passes from one medium to another, its speed and direction change due to differences in the refractive indices of the two media. This phenomenon is known as refraction.

Statement 1 is correct: In a denser medium (with a higher refractive index), light travels slower. When light moves into a less dense medium (with a lower refractive index), it speeds up. As a result, the light bends away from the normal (the imaginary line perpendicular to the surface at the point of incidence). The object appears to be closer from the surface than it actually is, as seen in the case of a coin in water when viewed from above.

Statement 2 is correct: If a person is underwater looking at a coin above the surface, the coin appears higher than its actual position, not lower. This is because light bends away from the normal when moving from water (denser) to air (rarer).

Explanation

Statement 1 is correct: The filament in a light bulb is typically made of tungsten. When the filament is not uniform, the thinner sections tend to heat up more, leading to higher temperatures and stress, which can cause premature failure.

Statement 2 is correct: Light bulbs typically contain an inert gas, like argon, to prevent oxidation of the filament and improve lifespan. Complete evacuation of the bulb is not possible. A small quantity of gases left behind which expands on heating by heat through filament. If the bulb is not evacuated properly, the filament would burn out quickly causing the bulb to have a short life.

Statement 3 is correct: The wires supporting the filament are designed to withstand high temperatures. However if they are not robust enough or if the filament heats up too much, and they can melt, causing the bulb to fail.

Explanation

Statement 1 is correct: Most car batteries are 12-volt lead-acid batteries. This is the standard voltage for automotive applications as it provides sufficient power for starting the engine and running electrical systems in vehicles.

Statement 2 is incorrect: The electrolyte used in a car battery is sulfuric acid (H₂SO₄), not hydrochloric acid. Sulfuric acid is mixed with distilled water to create the electrolyte solution, which facilitates the electrochemical reactions in the battery.

Statement 3 is incorrect: The electrodes in a car battery are made of lead (Pb) and lead dioxide (PbO), not copper. The negative electrode (anode) is made of pure lead, and the positive electrode (cathode) is made of lead dioxide.

Statement 4 is correct: The capacity of a car battery is expressed in ampere-hours (Ah). This unit measures the amount of charge a battery can deliver over time. For example, a 50 Ah battery can theoretically deliver 1 ampere of current for 50 hours or 5 amperes for 10 hours.

Explanation

Barium is used in X-ray imaging because it effectively absorbs X-rays, which makes it show up clearly on X-ray images. This property helps in creating a clear contrast between the stomach and surrounding tissues, allowing doctors to examine the stomach’s structure more easily.

Explanation

Cobalt-60 is a radioactive isotope that emits gamma rays. These high-energy rays are used in radiation therapy for cancer treatment because they can penetrate deep into tissues and target cancer cells effectively while minimizing damage to surrounding healthy tissues. Related terms:

Proton therapy is a type of cancer treatment that uses protons to precisely target and destroy tumor cells, minimizing damage to surrounding healthy tissues. It is particularly effective for tumors near sensitive areas, offering fewer side effects compared to conventional radiation therapy.

Explanation

Mycorrhiza is a symbiotic association between fungi and the roots of higher plants. In this relationship, the fungi help the plants by increasing water and nutrient absorption (especially phosphorus), while the plants provide carbohydrates (like glucose) to the fungi. This mutualistic relationship is beneficial to both organisms and plays a crucial role in plant growth and soil health.

Explanation

Endoscopy is a medical procedure that uses a flexible tube with a light and camera (endoscope) to explore the inside of the body, such as the stomach, intestines, or other organs. The technique relies on the phenomenon of total internal reflection to transmit light through fiber-optic cables inside the endoscope. Total internal reflection occurs when light traveling through a denser medium (such as glass or optical fibers) strikes the boundary with a less dense medium (like air) at a certain angle, causing the light to reflect entirely back into the denser medium instead of refracting out.

Explanation

Option (c) is correct: Formic acid is the substance that many ants inject when they bite. This acid is produced in their venom glands and is responsible for the characteristic pain or burning sensation felt after an ant bite. Formic acid is also used by ants for defense, and some species, like fire ants, use it in larger quantities to cause more intense reactions in their prey or threats.

Option (a), (b) and (d) are incorrect:

Acetic acid is a concentrated form of acetic acid, commonly found in vinegar, but it is not involved in the venom of ants. Methanol is a type of alcohol, not present in ant venom. Stearic acid is a fatty acid commonly found in animal fats and plant oils, but it is not the compound found in ant venom.