General Science GK Questions with Answers – Page 93

In a liquid the resistance to flow comes mainly from the attraction between neighbouring molecules. Heating gives the molecules energy to slip past one another, so the attraction matters less and the liquid thins; hot honey and warm engine oil pour far more easily than cold.

Evaporation is a surface phenomenon in which the fastest-moving molecules of a liquid break free. Doing so needs the latent heat of vaporisation, and that energy is drawn from the liquid left behind and from whatever the liquid touches, so both grow cooler.

This is the heat one gram of ice at 0 degrees Celsius must absorb to become one gram of water at 0 degrees Celsius; the temperature does not rise at all while it melts, because the energy goes into breaking the hydrogen-bonded lattice.

Bromine is a dark reddish-brown, dense, fuming liquid at ordinary room temperature, with a melting point of about minus 7 degrees Celsius and a boiling point of about 59 degrees Celsius.

Plasma is a hot, electrically conducting mixture of free electrons and positive ions produced when a gas is heated or strongly ionised.

Water contracts as it is cooled from higher temperatures like any other liquid, but only down to 4 degrees Celsius.

Boyle s law applies to a fixed mass of gas at constant temperature and states that pressure is inversely proportional to volume, so the product of the two is a constant: P1 into V1 equals P2 into V2.

In 1924 Satyendra Nath Bose sent Albert Einstein a paper deriving Planck s radiation law by counting indistinguishable light quanta.

A change of state is governed by the energy of the particles. When a solid absorbs heat its particles vibrate harder until the force holding them in the lattice is overcome and it melts; further heat lets the liquid particles escape as vapour.

Pinctada margaritifera is the black lip pearl oyster, a bivalve mollusc of the warm shallow water of the Indo-Pacific, where it fastens itself to coral reefs by strong threads.

Convection is the transfer of heat by the bodily movement of the particles of a fluid. The part that is heated expands, becomes lighter and rises, and colder, denser fluid sinks to take its place, so a circulating convection current is set up.

Bose designed the crescograph to magnify the growth of a plant many thousand times and record it on a smoked glass plate, which allowed him to show that plants respond to light, heat, touch and other stimuli in ways that resemble responses in animals.

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.

In 1895, while working with a discharge tube, Roentgen found an unknown radiation that passed through cardboard and flesh but was stopped by bone and metal, and made a screen coated with a fluorescent salt glow.

In 1928 Fleming noticed that a mould of the genus Penicillium which had contaminated a culture plate in his London laboratory had killed the staphylococcus bacteria around it, and he named the active substance penicillin.

A fathometer, also called an echo sounder, sends a pulse of sound from the hull of a ship to the sea floor and times the returning echo; since the speed of sound in sea water is known, the time gives the depth.

A lactometer is a floating instrument that measures the relative density of milk. Pure milk has a density slightly greater than that of water, so adding water lowers the reading and the float sinks deeper, which is how dilution is detected.

A barometer measures the pressure of the atmosphere, and the mercury barometer invented by Evangelista Torricelli in 1643 does so by balancing the weight of the air against a column of mercury about 76 centimetres high at sea level.

Elektron is the Greek name for amber, the fossilised tree resin which the ancient Greeks found would attract straw, feathers and bits of dust after being rubbed with fur.

Working independently in the 1830s, Michael Faraday in England and Joseph Henry in the United States showed that a changing magnetic flux through a circuit sets up an electromotive force in it, and that the effect depends on the rate of change of flux rather than on the flux itself.