General Science Previous Year Questions (PYQ) with Answers – Page 89

The Italian scientist Amedeo Avogadro proposed in 1811 that equal volumes of all gases, at the same temperature and pressure, hold the same number of molecules.

It is the heat a liquid absorbs to turn into vapour at its boiling point, while its temperature stays the same.

Specific heat capacity is the heat needed to raise the temperature of a unit mass of a substance by one degree, not simply the heat needed to raise its temperature.

Sodium hydroxide dissolves in water and splits completely into Na+ and OH- ions; the ions carry current and the hydroxide ions make the solution strongly basic.

At the boiling point, water turns into vapour inside the liquid itself, and these pockets of steam are the bubbles that rise and burst at the surface.

A rainbow forms because raindrops split white sunlight into its seven colours, and this splitting of light into colours is dispersion.

This statement is wrong because every photon, whatever its energy, travels in vacuum at the same speed of light, about 3 × 10^8 metres per second.

A p-type semiconductor is made by adding a small amount of a trivalent impurity, such as boron, aluminium, gallium or indium, to pure silicon or germanium.

Genuine currency notes carry security features printed with fluorescent inks that glow only under ultraviolet light, so a UV lamp quickly exposes a fake.

The human eye responds only to visible light, which lies roughly between 400 nm (violet) and 700 nm (red), and 500 nm is the only one of the three values in that range.

A convex mirror always forms an erect, diminished image, so it shows a much wider area of the road behind than a flat mirror of the same size, which is why it is used as a rear-view or side-view mirror.

Plant growth regulators, or plant hormones, are small molecules that control growth even in tiny amounts, and each main group comes from a different chemical family.

The SA node, a small patch of special muscle in the wall of the right atrium, produces the electrical impulse that starts each heartbeat, which is why it is called the pacemaker of the heart.

The Geiger-Müller counter detects and counts the ionising radiation given out by radioactive substances, so it is the standard instrument for measuring radioactivity.

Each product has been linked to the chemical paired with it. Lead has been found as a trace contaminant in many lipsticks, coming from colour pigments; since lipstick is swallowed in small amounts, regular use raises concern because lead is a toxic heavy metal that harms the nervous system.

Kwashiorkor is a disease of protein deficiency in a child who still gets enough calories. It usually appears when a child is weaned from breast milk onto a starchy diet with little protein.

Sunlight takes about 8 minutes and 20 seconds, roughly 500 seconds, to travel from the Sun to the Earth. The average distance between the Sun and the Earth is about 150 million kilometres, a distance called one astronomical unit.

Biogas is mainly methane and carbon dioxide. Biogas is produced when bacteria break down animal dung, crop waste and kitchen waste in the absence of oxygen, a process called anaerobic digestion.

When light of a suitable frequency falls on a metal and knocks electrons out of it, the process is called photoelectric emission.

Carborundum, or silicon carbide (SiC), is one of the hardest substances known, so it can grind, cut and polish other materials, which is what an abrasive must do.