General Science Mixed Quiz: Set 176

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.

A beam seen from the side is visible only because tiny particles send some of its light sideways. Light travelling in a straight line cannot enter our eyes unless something redirects it towards us.

Temporary hardness is caused by the bicarbonates (hydrogencarbonates) of calcium and magnesium dissolved in water. It is called temporary because it can be removed simply by boiling: on heating, the soluble bicarbonates break down into insoluble carbonates, or magnesium hydroxide, which settle out, and carbon dioxide escapes.

Gamma rays sit at the far end of the electromagnetic spectrum, with the shortest wavelength and therefore the highest frequency and energy.

Phytoplasmas are bacteria without cell walls that live in the food-conducting tissue of the plant, and they are carried from plant to plant by sap-sucking leafhoppers, also called jassids; in little leaf of brinjal the leaves become very small and numerous, the plant bushes out and no fruit is set.

One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second.

By Einstein's photoelectric equation, the photon gives energy equal to Planck's constant times the frequency, part of which is spent as the work function, so the maximum kinetic energy left with the electron rises with frequency and is independent of how bright the light is.

The earth is flattened at the poles, so the distance from the centre is least there, and since g varies inversely as the square of that distance, g is largest at the poles.

The formula of ammonia is NH3, so its molecular mass is the atomic mass of one nitrogen atom added to the atomic masses of three hydrogen atoms, that is fourteen plus three times one, which equals seventeen unified atomic mass units; one mole of ammonia therefore weighs seventeen grams.

Iodine is needed to make thyroxine, so when the diet is short of it the thyroid gland works harder and enlarges into a visible swelling of the neck called goitre; a severe shortage in a growing child causes cretinism and in an adult myxoedema, and iodised salt is the standard…

Clean sand is made almost entirely of quartz, which is silica or silicon dioxide, and silica is the main ingredient of glass.

Vitamin D helps the intestine absorb calcium and phosphorus, so without it the bones of a growing child stay soft and bend, giving bow legs, a pigeon chest and a large forehead; this disease is rickets.

Root-knot is caused by microscopic soil roundworms of the genus Meloidogyne, which enter the young root, settle in it and make the surrounding tissue swell into knots or galls; the plant then cannot draw water properly and wilts in the afternoon heat even when the soil is moist.

In a dihybrid cross two pairs of characters are followed together, for example seed shape and seed colour, and the appearance of all four combinations in the proportion nine to three to three to one shows that the inheritance of one pair does not depend on the inheritance of the…

The work function of a metal is the least energy needed to free an electron from its surface, and it is equal to Planck's constant multiplied by the threshold frequency of that metal; caesium and potassium have low work functions, which is why they respond to visible light.

A seismograph holds a heavy mass that tends to stay still while the ground and the frame of the instrument move during a tremor; the relative motion is magnified and traced as a seismogram, from which the arrival times of the primary, secondary and surface waves are read.

Calcium chloride is an ionic compound, so the sum of the atomic masses in its formula is called the formula unit mass rather than the molecular mass.

Birds, blowing dust, rain and wind can all carry the agents of plant disease from one plant to another. Plant pathogens such as fungi, bacteria and viruses cannot move on their own over long distances, so they depend on carriers.

The device works by stimulated emission, in which a photon passing an excited atom makes it fall to a lower level and emit a second photon identical in frequency, phase and direction, so one photon becomes two and the light is amplified.

It is the number of atoms in twelve grams of carbon twelve, and it holds for atoms, molecules, ions or electrons alike, so one mole of water has that many water molecules and one mole of sodium has that many sodium atoms.