General Science Mixed Quiz: Set 206

The object lies between F and 2F of the convex lens (25 cm and 50 cm), and such an object always gives a real, inverted and enlarged image beyond 2F. Using the lens formula 1/v − 1/u = 1/f with u = −40 cm and f = +25 cm gives…

Pearls are harvested from pearl oysters, which are bivalve molluscs. When a foreign particle, such as a grain of sand or a parasite, gets inside the shell, the oyster's mantle covers it layer after layer with nacre, the shiny material also called mother of pearl.

An echo is sound that bounces back from a hard surface such as a wall, cliff or hill and reaches our ears again.

Egg white is mostly water and protein, and heat denatures these proteins so that they set into an opaque white solid.

This reverses the truth: a voltmeter has a very high resistance and an ammeter a very low one. An ammeter measures the current flowing through a circuit, so it is placed in series and the whole current passes through it.

Chemical messengers called neurotransmitters are released from the nerve endings, the tips of the axon, into the synapse. A nerve impulse travels from the dendrites through the cell body and along the axon as an electrical signal.

On the pH scale every value below 7 means the solution has more hydrogen ions than hydroxide ions, which is what makes it acidic.

Darwin set out in that book the theory of evolution by natural selection, drawing on observations made during his voyage on HMS Beagle, among them the finches of the Galapagos islands whose beaks differ with their diet.

A desiccant is a substance that absorbs moisture from its surroundings and keeps things dry, and silica gel is the most widely used one.

The retina is the light-sensitive layer at the back of the human eye; it is not a part of any microscope.

Proteins are made on ribosomes, and the smooth endoplasmic reticulum has no ribosomes on its surface. The endoplasmic reticulum is a network of membrane tubes and sacs in the cytoplasm.

A nuclear reactor splits heavy nuclei such as uranium-235 in a chain reaction that is kept under control, releasing heat at a steady rate.

Silver is less dense, so a silver piece takes up more volume, loses more weight to buoyancy in water, and must therefore be heavier in air to show the same weight under water.

The base is made thin and lightly doped so that most charge carriers from the emitter cross it to the collector.

In glass, light of shorter wavelength travels more slowly, so the glass has a higher refractive index for it and bends it more.

Nichrome is an alloy of nickel, chromium and iron with a high electrical resistance and a high melting point, and it does not oxidise easily when red hot, so a nichrome wire can glow for years without burning away; that combination makes it the standard material for the heating elements…

Lactobacillus turns the lactose sugar of milk into lactic acid, which sours the milk and makes it set into curd.

The ABO system sorts blood by the antigens present on the surface of red blood cells, and it has exactly these four groups.

Apart from the Sun, Proxima Centauri is the star nearest to the Earth, about 4.24 light years away. Proxima Centauri is a small, dim red dwarf in the constellation Centaurus and cannot be seen with the naked eye.

Oxygen makes up about 21 per cent of dry air by volume, second only to nitrogen. Dry air near the ground is about 78 per cent nitrogen, 21 per cent oxygen and 0.93 per cent argon, which is the third most abundant gas.