General Science Mixed Quiz: Set 203

A light year is the distance that light travels in empty space in one year, so despite the word "year" it measures length, not time.

Melting of ice only changes the state of water from solid to liquid; no new substance is formed, so it is a physical change.

Friction is a non-conservative force because the work it does depends on the path taken and the energy it removes is lost as heat.

Cohesive forces pull the molecules at the surface of a liquid inward, so the surface behaves like a stretched membrane and takes the smallest area that can enclose the given volume; for a fixed volume the shape of least surface area is a sphere, which is why a free drop…

Light travels fastest in a vacuum; in any material medium, including carbon disulphide, it slows down, so its speed there (X) is less than its speed in vacuum (Y).

Quartz is crystalline silicon dioxide (SiO₂), an electrical insulator, not a semiconductor. A semiconductor has a conductivity between that of a conductor and an insulator, and its conductivity rises with temperature or when impurities are added (doping).

The speed of sound in air increases, not decreases, as temperature rises, so statement B is the incorrect one. Sound in a gas travels faster when the gas is warmer, because its molecules move faster and pass the vibration on more quickly.

Limestone decomposes in the furnace to calcium oxide, a basic flux, which combines with the acidic silica gangue of the ore to form calcium silicate, a fusible slag that floats on the molten iron and is drawn off separately.

The bulb's resistance stays the same, and since power varies as the square of voltage, halving the voltage cuts the power to one-fourth.

A good fuel should have a moderate ignition temperature, not a very low one.

Hair turns grey because the chemical make-up of the hair changes as the body stops producing the pigment melanin, so new substances form and the change cannot be reversed.

Polythene, also written polyethene, is formed by the addition polymerisation of ethene, in which the double bond of each molecule opens and the units join into a long chain with nothing eliminated.

A soda-acid extinguisher holds a solution of sodium hydrogen carbonate (baking soda) and a small bottle of sulphuric acid; when the two mix, carbon dioxide is released.

Autotrophs take carbon dioxide from their surroundings and build their own organic food from it, so CO₂ is their main source of carbon.

Silver reacts with traces of hydrogen sulphide in the air and forms a black coating of silver sulphide. This slow attack on a metal by its surroundings is called corrosion, and on silver it is usually called tarnishing.

A whale is a mammal, not a fish, so it breathes with lungs and must come to the surface to take air through a blowhole on top of its head.

H₂S is a colourless gas with the familiar smell of rotten eggs, and the human nose can detect it even in very small amounts.

Neither statement is correct: only starch is a mixture of amylose and amylopectin, and only glycogen is stored in liver cells.

Villi are tiny finger-like folds of the inner lining of the small intestine that greatly increase its surface for absorbing digested food.

An ECG records the electrical signals that make the heart muscle contract with each beat. Each heartbeat starts at the sino-atrial (SA) node, the natural pacemaker in the right atrium.