General Science Previous Year Questions (PYQ) with Answers – Page 63

LIGO uses laser beams in long perpendicular arms to detect the tiny stretching of space caused by gravitational waves. LIGO has two detectors in the United States, at Hanford in Washington and Livingston in Louisiana, each with arms 4 km long.

Red light has the longest wavelength in the visible spectrum, so glass slows it the least and bends it the least.

A black hole forms when a very massive star collapses under its own gravity, and its pull becomes so strong that not even light can escape.

When a magnet moves inside a coil, the magnetic flux linked with the coil changes, and this change produces an electromotive force and a current.

The statement is wrong because the inner wall of a thermos flask is silvered so that it radiates very little heat; the shiny outer surface also reflects heat back rather than absorbing it.

Particles of matter mix with one another on their own, and there are forces of attraction between them; both are basic properties taught in Class 9 science.

Air near the ground is denser than air higher up, so sunlight bends as it passes through the atmosphere and reaches us while the Sun is still just below the horizon.

Tooth enamel is made mainly of calcium phosphate in the form of a hard crystal called hydroxyapatite. Enamel is the hardest substance in the human body, harder even than bone.

When three forces are represented by the sides of a triangle taken in order, their vector sum is zero, because the three sides close the triangle, so the body cannot be pushed away; but the lines of action are different, so the system reduces to a couple.

Farmyard manure is the decomposed mixture of cattle dung, urine and bedding litter, and in general it carries only about half a per cent of nitrogen, along with roughly the same order of phosphate and potash.

Nitrogen, phosphorus and potassium are the three primary nutrients, and a fertiliser that carries two or more of them in one chemical compound is called a complex or mixed fertiliser; diammonium phosphate, which supplies both nitrogen and phosphate, and the NPK grades sold by number are the familiar examples.

Sleeping sickness, or African trypanosomiasis, is caused by the protozoan parasite Trypanosoma brucei, which is spread by the bite of the tsetse fly.

Ice is simply water in its solid state, a single compound with the fixed formula H2O, so it is a pure substance, not a mixture.

Quick lime is calcium oxide (CaO), which contains no carbonate, so it gives no carbon dioxide with an acid. Acids release carbon dioxide only from carbonates and hydrogencarbonates: the general reaction is metal carbonate plus acid gives salt, water and carbon dioxide.

Photosynthetic bacteria have no chloroplasts; their pigments sit on infoldings of the cell membrane that form vesicles or sacs, often called chromatophores.

The truth is the reverse: hepatitis B has a safe, effective vaccine, while hepatitis C has none. The hepatitis B vaccine has been in use since the 1980s and is given to newborns in India under the Universal Immunisation Programme, with the first dose soon after birth.

Drug resistance grows in microbes when antibiotics are misused, and both wrong doses and farm use of antibiotics are forms of misuse.

Evaporation is a surface process, so its rate depends on conditions at the surface of the liquid, not on how much liquid there is in total.

When copper is left in moist air for a long time, it slowly reacts with oxygen, water vapour and carbon dioxide.

Friction acts along the surfaces in contact, opposite to the direction of motion, not along the line joining the centres of two bodies, so it is non-central.