Scientific Instruments and Discoveries: Notes and PYQs

The correct answer is D, J. J. Thomson. In 1897 Thomson passed an electric discharge through a gas at very low pressure and showed that the cathode rays produced were a stream of identical negatively charged particles, far lighter than any atom and the same whatever gas or electrode was used. He called them corpuscles; they were later named electrons, and he measured their charge to mass ratio. Option A, Chadwick, discovered the neutron in 1932 and not the electron. Option B, Niels Bohr, did not discover any particle; he proposed the model in which electrons revolve in fixed energy shells and explained the hydrogen spectrum. Option C, Rutherford, used the scattering of alpha particles by gold foil to establish the small, dense, positively charged nucleus and gave the proton its name. The order to memorise is electron by Thomson in 1897, nucleus and proton by Rutherford, and neutron by Chadwick in 1932.

The correct answer is C, James Chadwick. In 1932 Chadwick bombarded beryllium with alpha particles and showed that the highly penetrating radiation given off consisted of neutral particles with almost the same mass as a proton. The neutron explained why the mass of an atom is greater than the mass of its protons, and it explained isotopes, so Chadwick received the Nobel Prize in Physics for it. Option A, Marie Curie, worked on radioactivity with her husband Pierre and isolated polonium and radium; she did not discover a nuclear particle. Option B, Rutherford, discovered the nucleus through the gold foil experiment and predicted that a neutral particle must exist, but it was his student Chadwick who found it. Option D, Max Planck, founded the quantum theory by proposing that energy is radiated in packets called quanta. The three-line summary is Thomson for the electron, Rutherford for the nucleus and Chadwick for the neutron.

The correct answer is C, Faraday and Henry. 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. This single result is the basis of the dynamo, the alternating current generator, the transformer and the induction motor, and the unit of inductance, the henry, is named after Henry. Option A, Rutherford, belongs to nuclear physics and not to electromagnetism. Option B, Einstein, is remembered for the photoelectric effect, for relativity and for the mass energy relation. Option D pairs Planck, the founder of quantum theory, with Fermi, who built the first nuclear reactor, neither of whom worked on induction. Remember that Faraday also gave the laws of electrolysis, so his name appears in chemistry questions too.

The correct answer is B, amber. 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. Because amber was the first material in which this attraction was noticed, the whole science that grew out of it was named electricity, and the particle Thomson discovered in 1897 was named the electron. Option A, ebonite, is a hard vulcanised rubber used in school experiments on static electricity; it is a modern material and not the source of the word. Option C, charge, is the physical quantity that the phenomenon involves, but it is not what the Greek word means. Option D, negative, describes the sign of the charge an electron carries, which was fixed by convention long after the Greek word was coined. Questions on the origin of scientific words are set often, so remember amber for elektron and atomos, meaning indivisible, for atom.

The correct answer is B, barometer. 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. A sudden fall in the reading means that a storm is approaching, while a steady high reading means fine weather, so the instrument is the foundation of weather forecasting. Option A, hygrometer, measures the humidity or the amount of water vapour in the air. Option C, anemometer, measures the speed of the wind, usually with three or four cups that spin on a vertical axis. Option D, lactometer, measures the relative density of milk and so indicates whether it has been diluted. The trap to watch for is manometer, which also measures pressure but the pressure of an enclosed gas rather than that of the open atmosphere.

The correct answer is B, lactometer. 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. Option A, hydrometer, is the general instrument for the relative density of any liquid, and the lactometer is in fact a hydrometer graduated specially for milk; in a question that offers both, the specific instrument is the expected answer. Option C, calorimeter, is a vessel used to measure quantities of heat in experiments on specific heat capacity and latent heat. Option D, spherometer, measures the radius of curvature of a spherical surface such as a lens, using three fixed legs and a central screw. Note that a lactometer shows whether milk has been watered down, but it cannot by itself prove that milk is free of all adulterants.

The correct answer is B, fathometer. 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. The name comes from the fathom, the old unit of six feet used for soundings. Option A, altimeter, measures height above sea level and is fitted in aircraft, where it works from the fall of atmospheric pressure with altitude. Option C, tachometer, measures the rate of rotation of a shaft in revolutions per minute and is fitted to engines and turbines. Option D, audiometer, measures the sharpness of a person's hearing across a range of frequencies. A related instrument worth remembering is the hydrophone, which detects sound under water, and sonar, which uses the same echo principle to locate submarines and shoals of fish.

The correct answer is B, Alexander Fleming. 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. Howard Florey and Ernst Chain later purified it and made mass production possible, and the three shared the Nobel Prize in Medicine. Option A, Louis Pasteur, established the germ theory of disease, developed pasteurisation and made vaccines for rabies and anthrax, but not penicillin. Option C, Robert Koch, identified the bacteria that cause tuberculosis, cholera and anthrax and framed the postulates that link a microbe to a disease. Option D, Edward Jenner, introduced vaccination in 1796 using cowpox material to protect against smallpox and is called the father of immunology. Papers often group these four names together, so fix one achievement firmly against each.

The correct answer is A, Wilhelm Conrad Roentgen. 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. He called it the X-ray because its nature was unknown, and he received the first Nobel Prize in Physics in 1901. Option B, Henri Becquerel, discovered radioactivity the following year, in 1896, when uranium salts fogged a photographic plate kept in the dark, which is a different phenomenon from X-rays. Option C, Marie Curie, with Pierre Curie isolated polonium and radium and coined the word radioactivity, and she remains the only person to win Nobel Prizes in two different sciences. Option D, Thomas Edison, was an inventor of the electric lamp, the phonograph and the carbon microphone. Keep the years apart: X-rays in 1895 and radioactivity in 1896.

The correct answer is B, waves of an earthquake. 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. Those arrival times at three or more stations give the location of the focus, and the amplitude gives the magnitude on the Richter scale, while intensity is described on the Mercalli scale. Option A, humidity, is measured by a hygrometer. Option C, intensity of light, is measured by a photometer or a lux meter. Option D is tested chemically and by instruments such as a turbidity meter, not by a seismograph. A connected fact asked often is that primary waves are longitudinal and travel through solids and liquids, while secondary waves are transverse and cannot pass through a liquid.

The correct answer is A, Jagadish Chandra Bose. 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. He also did pioneering work on millimetre wave radio and founded the Bose Institute in Kolkata. Option B, Satyendra Nath Bose, is remembered in physics for Bose Einstein statistics and for the class of particles called bosons. Option C, Homi Jehangir Bhabha, founded the Tata Institute of Fundamental Research and the Indian atomic energy programme and is called the father of the Indian nuclear programme. Option D, Prafulla Chandra Ray, was a chemist who discovered mercurous nitrite and founded Bengal Chemicals, and he wrote a history of Hindu chemistry. Indian scientist questions appear in almost every general awareness paper, so keep one instrument or theory against each name.