Optics
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50 free Optics trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Optics is the science of light: why a spoon looks bent in a glass of water, how a curved piece of glass can start a fire or sharpen blurred sight, and why the sky changes colour at dusk. Almost everything we know about the universe, from distant galaxies to the smallest living things, reached us through an instrument that bends or bounces light. This quiz covers the ground a first course on light does. There are questions on reflection in flat and curved mirrors, on how lenses bend light, on colour and the spectrum, on the human eye, and on instruments from spectacles to space telescopes. The people are here too: the experimenters who split sunlight, timed it, and argued for centuries over whether it is a wave or a stream of particles. The opening questions suit children and anyone meeting the subject for the first time. Later ones step up to the level of a school physics class, with a few for enthusiasts. Every answer comes with a short explanation, so a miss still teaches you something.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which vehicle's name is often painted in reverse so that drivers ahead can read it in a mirror?
Ambulance
Ambulance is spelled out in mirror writing so the word reads the right way round in a rear-view mirror. Leonardo da Vinci wrote most of his personal notes in the same reversed script.
Q 02Which legume gave the lens its Latin name, because a lens bulging on both sides has the same shape?
Lentil
Lentil in Latin is simply lens. English borrowed the word in the 1690s for glass that regulates light rays, by analogy with the shape of the seed.
Q 03How long does sunlight take to reach Earth, when light from the next nearest star takes over four years?
8 minutes
8 minutes is the trip through space, so we see the Sun as it was a little while ago. The energy first spends 10,000 to 170,000 years working its way out from the Sun's centre.
Q 04Which colour appears on a screen when red and green light are combined at equal intensity?
Yellow
Yellow is a secondary colour of light, made on screens whose pixels glow only red, green and blue. Cyan and magenta are the other two secondaries.
Q 05Which Founding Father is generally credited with inventing bifocal glasses for near and far vision?
Benjamin Franklin
Benjamin Franklin was one of the first people known to wear split lenses. One account says he cut his lenses in half so he could lip-read French speakers at court.
Q 06Which space telescope launched in 1990 with a misshapen main mirror that astronauts fixed in 1993?
Hubble
Hubble's main mirror was smooth to about 10 billionths of a metre, yet its outer edge was too flat by roughly two thousandths of a millimetre, enough to blur its view.
Q 07In a doubtful legend, which Greek inventor burned Roman ships at Syracuse using mirrors and sunlight?
Archimedes
Archimedes gets the credit only in later tellings: none of the three earliest accounts of the siege, by Polybius, Livy and Plutarch, mentions mirrors.
Q 08Which colour, named after a plant dye, sits between blue and violet in the seven-colour spectrum?
Indigo
Indigo joined the list in the 1600s, when the spectrum's colours were matched to the seven notes of a musical scale. Some scientists think that indigo was simply what we now call blue.
Q 09Which effect, caused by light bending through hot air, makes a distant road look covered in water?
Mirage
Mirage images are real enough to photograph: the water is light from the sky, bent by the hot air just above the road. Only the mind's reading of it as a puddle is wrong.
Q 10Which toy, invented by David Brewster, uses tilted mirrors to turn beads into symmetrical patterns?
Kaleidoscope
Kaleidoscope was Brewster's own coinage, from Greek words meaning the observation of beautiful forms. He hit on the idea in 1814 while experimenting with light bouncing between glass plates.
Q 11Which sky sight always appears opposite the Sun and looks like a full circle from an aircraft?
Rainbow
Rainbow light is bent on entering a water droplet, bounced off the back of it and bent again on the way out. From the ground only an arc of the circle is usually visible.
Q 12Which word describes the bending of light that makes a pencil in water look broken at the surface?
Refraction
Refraction happens because light changes speed as it passes from one material into another. The same bending makes a pool look shallower than it really is.
Q 13Which English scientist split white light with one prism and recombined the colours with another?
Isaac Newton
Q 21Which mirror shape is used for shop security mirrors because it shows a wider view than a flat one?
Convex
Convex mirrors make everything look smaller, which fits more of the scene in. That is why some car wing mirrors carry a warning that objects are closer than they appear.
Q 22Which eye condition blurs distant objects but not near ones, and is corrected with concave lenses?
Myopia
Myopia was named by the physician Galen, from Greek words meaning to close the eye. Johannes Kepler later showed that lenses curving inward could correct it.
Q 23Which name, popularised by chemist Gilbert Lewis in 1926, is given to a single particle of light?
Photon
Photon particles are massless, so they can only move at one speed, the speed of light in a vacuum. The idea of light as units of energy grew out of work on the photoelectric effect.
Isaac Newton gave the band of colours its name, spectrum. In 1668 he also completed the earliest known working reflecting telescope, which gathers light with a mirror instead of a lens.
Q 14Which astronomer made his own telescope in 1609 and soon discovered Jupiter's four largest moons?
Galileo Galilei
Galileo Galilei at first described the moons as three fixed stars lying in a line through Jupiter. Their shifting positions over the next nights showed him they were orbiting the planet.
Q 15Which light-sensitive layer at the back of the eye plays the role of film or a sensor in a camera?
Retina
Retina tissue grows out of the developing brain in the embryo, so it counts as part of the central nervous system. It is, in effect, brain tissue at the back of the eye.
Q 16Which French mathematician proposed in 1662 that light follows the path that takes the least time?
Pierre de Fermat
Pierre de Fermat proposed it to explain how light bends between two materials. The idea was controversial at first because it seemed to credit nature with knowledge and intent.
Q 17Which instrument uses two parallel mirrors set at 45 degrees to let a hidden viewer see over walls?
Periscope
Periscope tubes with two added lenses let soldiers keep watch from the trenches of World War I. Submarine versions swap the mirrors for prisms and add magnification.
Q 18Which gemstone's high dispersion splits white light into flashes of colour that jewellers call fire?
Diamond
Diamond shows little of this as a rough stone, so it has to be cut and polished. In 1919 Marcel Tolkowsky calculated a cut that balances white brilliance against coloured fire.
Q 19Which physicist won a Nobel Prize for explaining the photoelectric effect rather than for relativity?
Albert Einstein
Albert Einstein proposed in 1905 that light itself consists of localized particles. Nearly all physicists rejected the idea at first, including Max Planck and Niels Bohr.
Q 20Which word describes frosted glass, which lets light through but scatters it so that images blur?
Translucent
Translucent comes from Latin words meaning to shine through. Glass is frosted by sandblasting or acid etching, which pits one side so that it scatters light instead of passing a clear image.
Q 24Which precious metal coats the glass in the mirror design credited to Justus von Liebig in 1835?
Silver
Silver had long been polished into mirrors on its own, and such mirrors were in wide use in the Roman Empire. Many modern mirrors use a thin coating of aluminium instead.
Q 25Which handheld instrument has prisms inside each barrel to turn the image the right way up?
Binoculars
Binoculars built with prisms also became shorter, since the light path is folded inside. Until the 1890s the same job was done by long twin telescopes with extra lenses.
Q 26In which country were the first eyeglasses made around 1290, according to a friar's sermon of 1306?
Italy
Italy has the evidence in that sermon, in which Giordano da Pisa said the art of making glasses was not yet twenty years old. Venice had rules on selling them by 1301.
Q 27Which type of sunglasses lens, first sold in 1936 with Edwin Land's filter, cuts glare off water?
Polarized
Polarized lenses block glare reflected at some angles off shiny non-metallic surfaces. Edwin Land gave his patented filter a brand name that became famous: Polaroid.
Q 28Which type of three-dimensional image, recorded with laser light, won Dennis Gabor a Nobel Prize?
Hologram
Hologram research began as a side effect in 1948, when Gabor was looking for a way to improve image resolution in electron microscopes. The field took off only after the laser arrived in 1960.
Q 29Which structures were the stepped lenses of physicist Augustin-Jean Fresnel designed to be used in?
Lighthouses
Lighthouses gave the design its nickname, the invention that saved a million ships. The first one was lit in July 1823, and single-piece versions later went into car headlamps.
Q 30Which law of light bending bears a Dutch astronomer's name, though Ibn Sahl found it in Baghdad in 984?
Snell's law
Snell's law went unpublished in the lifetime of Willebrord Snellius, who derived it in 1621. René Descartes reached it independently and printed it in 1637.