General Science Previous Year Questions (PYQ) with Answers – Page 50

At this one temperature the Celsius and Fahrenheit scales show the same number. The two scales are linked by F = (9/5)C + 32.

This is absolute zero, more exactly −273.15°C or 0 kelvin, the temperature below which nothing can be cooled. Temperature measures the random motion of particles.

Light travels at different speeds in different media, and this change in speed at the boundary makes it bend. Light is fastest in vacuum, about 3 × 10⁸ m/s, and slower in water and glass.

Electric power is voltage multiplied by current, and 110 V × 0.2 A = 22 W. Power is the rate at which electrical energy is used.

The oyster feeds by drawing water over its gills and straining out plankton and organic particles, which is filter feeding.

An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.

Magnesium, calcium and barium are all alkaline earth metals of group 2, and each has a valency of 2. Elements in the same group of the periodic table have the same number of electrons in their outermost shell, and so the same valency.

The wave travels at 1,200 m/s, so 2,400 m takes 2 seconds. The speed of any wave is the product of its frequency and wavelength: v = fλ.

All three are fungi that feed saprophytically: they release enzymes onto dead organic matter, digest it outside their bodies and then absorb the dissolved food.

Atoms get smaller along a period and larger down a group. Moving from left to right in a period, electrons are added to the same shell while the nuclear charge rises by one at each step.

Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.

Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.

Traditional solder is an alloy of lead and tin, often in a ratio of about 60 parts tin to 40 parts lead.

In the electrolytic refining of copper, a solution of copper sulphate made acidic with a little dilute sulphuric acid carries the copper ions between the electrodes.

The pulmonary veins carry oxygen-rich blood from the lungs into the left atrium. In double circulation, blood passes through the heart twice in each full round.

Reducing manganese dioxide with aluminium, 3MnO₂ + 4Al → 3Mn + 2Al₂O₃, gives out a large amount of heat. This method of reducing a metal oxide with aluminium powder is called aluminothermy, or the Goldschmidt thermite process.

Sodium reacts vigorously with cold water to form sodium hydroxide and hydrogen gas: 2Na + 2H₂O → 2NaOH + H₂.

Gold is a noble metal at the bottom of the reactivity series, so it does not react with oxygen, water or ordinary acids.

Holothuria, the sea cucumber, is an echinoderm, a non-chordate group, so it never has a notochord at any stage of life.

Furnace oil is a heavy refinery product, it is burnt by industry for heat and power, and its high sulphur content makes it a polluting fuel.