Electromagnetic Spectrum
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50 free Electromagnetic Spectrum trivia questions with answers — science & nature quiz, new questions added Oct 2026.
Visible light is only a sliver of something much bigger. The electromagnetic spectrum runs from radio waves longer than a football pitch to gamma rays smaller than an atom, and every band is the same kind of wave, differing only in wavelength, frequency and the energy it carries. That one idea links a kitchen appliance, a hospital scan, a sunburn and a signal from the far side of the universe. This quiz covers the whole range the way a school science unit does, then goes further: how the waves behave, everyday uses from wireless gadgets to medical imaging, what sunlight does to skin, and the observatories that study the sky in light our eyes cannot see. A run of harder questions meets the scientists who found each invisible band. It suits students revising waves for a physics or astronomy test, teachers who want a ready-made review round, and quiz fans curious about how the invisible world works. Every answer comes with a short explanation.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Percy Spencer, whose candy bar reportedly melted beside a radar set, first deliberately microwaved which food?
Popcorn
Popcorn was the first food Spencer cooked on purpose; the second was an egg, which exploded in the face of a fellow experimenter.
Q 02The first X-ray photograph of a human body, taken in December 1895, showed which part of the physicist's wife?
Her hand
Her hand was the subject, and on seeing her own skeleton Anna Bertha is said to have exclaimed, "I have seen my death!"
Q 03Which nutrient, needed for strong bones, does human skin make when ultraviolet B rays in sunlight strike it?
Vitamin D
Vitamin D forms when UVB strikes a cholesterol-like compound in the skin, and because window glass blocks almost all UVB, sunshine through a window does not do the job.
Q 04Which space telescope, launched on Christmas Day 2021, has a gold-coated mirror built to observe infrared light?
James Webb
James Webb carries 18 hexagonal mirror segments plated in gold, a metal chosen because it reflects infrared light so well.
Q 05Which short-range radio technology is named after a tenth-century king who united Denmark's tribes?
Bluetooth
Bluetooth takes its name from King Harald Bluetooth, and its logo is a bind rune that merges the runes for his two initials.
Q 06Which everyday household gadget sends its commands as coded pulses of invisible infrared light?
TV remote control
TV remote control signals are invisible to the eye, yet a phone camera pointed at the handset will often show them flashing.
Q 07Which gas high in Earth's atmosphere absorbs most of the Sun's harmful ultraviolet radiation?
Ozone
Ozone in this layer soaks up 97 to 99 percent of the Sun's medium-frequency ultraviolet light, which would otherwise damage life at the surface.
Q 08Photo 51, an X-ray image taken under Rosalind Franklin's supervision in 1952, revealed the structure of which molecule?
DNA
DNA was the molecule, and the photo, the 51st in its series, was shown to rival researcher Watson without Franklin's permission.
Q 09From the 1920s, which kind of shop let customers view their own bones through an X-ray machine?
Shoe shops
Shoe shops used the fluoroscope so parents could watch a child's toes wiggle inside a new pair, but tests in 1948 found the machines poor at fitting.
Q 10Which home wireless technology shares the 2.4 GHz band with microwave ovens and may slow when one is running?
Wi-Fi
Wi-Fi can stutter because the ovens cook at about 2.45 GHz, and the small amount of radiation that escapes lands on the same waveband.
Q 11Which astronomer, the discoverer of Uranus, found infrared in 1800 with a thermometer placed just beyond red sunlight?
William Herschel
William Herschel called his find "calorific rays", and his studies led to the finding that slightly more than half of the Sun's energy reaching Earth is infrared.
Q 12Which German physicist won the very first Nobel Prize in Physics, in 1901, for discovering X-rays?
Wilhelm Röntgen
Wilhelm Röntgen refused to patent the discovery so that society as a whole could benefit, and he was so shy of public speaking that he declined to give a Nobel lecture.
Q 13Which German physicist, whose name is now the unit of frequency, first produced radio waves in the 1880s?
Heinrich Hertz
Q 21Which leftover glow of the Big Bang did Penzias and Wilson first suspect was pigeon droppings fouling their antenna?
Cosmic microwave background
The cosmic microwave background hiss stayed put after the birds were evicted and the antenna scrubbed, and the accidental find won the 1978 Nobel Prize in Physics.
Q 22Which spinning stars, found by Jocelyn Bell in 1967, sent radio blips so regular they were nicknamed "Little Green Men"?
Pulsars
Pulsars tick so steadily, the first one every 1.337 seconds, that Bell's supervisor at first dismissed the signal as radio interference.
Q 23US Vela satellites, built to catch secret Soviet nuclear tests, instead discovered which cosmic explosions in 1967?
Heinrich Hertz did not realize the practical importance of what he had done, reportedly calling the experiment "of no use whatsoever" beyond proving a theory right.
Q 14Which Scottish physicist showed in the 1860s that light is a wave of electric and magnetic fields?
James Clerk Maxwell
James Clerk Maxwell found that electric and magnetic fields travel together as waves at the speed of light; Einstein called his work the most profound since Newton.
Q 15Radio waves and gamma rays cross empty space at the same speed, roughly how many kilometres per second?
300,000
300,000 kilometres per second, or about a billion kilometres per hour, is the one speed that every kind of electromagnetic wave shares in a vacuum.
Q 16Which glass object did Isaac Newton use in the 1660s to split a beam of sunlight into a band of colours?
A prism
A prism did the splitting, and Newton, who named the resulting band a spectrum, then used a lens and a second one to blend the colours back into white light.
Q 17Which process warms Earth as gases such as carbon dioxide absorb infrared radiation rising from the ground?
Greenhouse effect
The greenhouse effect works because the atmosphere absorbs about 90% of the longwave radiation the surface gives off but only 23% of incoming sunlight.
Q 18Which pigment does human skin make more of after exposure to ultraviolet rays, producing a suntan?
Melanin
Melanin acts as a built-in sunscreen: its dark form, eumelanin, can dissipate more than 99.9% of the UV radiation it absorbs.
Q 19Which hospital machine builds images from pulses of radio waves inside a strong magnet, with no X-rays involved?
MRI scanner
An MRI scanner spares the patient the radiation dose of CT and PET scans; the trade-off is a longer, louder stay inside a confining tube.
Q 20Which scientist equipped a fleet of mobile X-ray vans for French field hospitals during World War I?
Marie Curie
Marie Curie's vans became known as petites Curies, or "Little Curies", and her X-ray units are estimated to have treated over a million wounded soldiers.
Gamma-ray bursts
Gamma-ray bursts first showed up on 2 July 1967 as a flash unlike any known weapon signature, and the discovery was not published until 1973.
Q 24What do astronomers call the stretching of light from distant galaxies to longer wavelengths as the universe expands?
Redshift
Redshift readings let Edwin Hubble report in 1929 that the more distant a galaxy is, the more its light is stretched, a rule now called Hubble's law.
Q 25Which element was first detected as a yellow line in sunlight during an 1868 eclipse, before being found on Earth?
Helium
Helium takes its name from helios, the Greek word for the Sun, because Norman Lockyer argued the line came from a new element; chemists only isolated it in 1895.
Q 26Radio astronomy began in the 1930s when Bell Labs engineer Karl Jansky traced a faint hiss of static to which source?
The Milky Way
The Milky Way was the source, strongest toward the constellation Sagittarius; Jansky had only been asked to hunt down static that might spoil radio telephone calls.
Q 27Which planet-wide network of radio dishes produced the first image of a black hole in 2019?
Event Horizon Telescope
The Event Horizon Telescope links radio dishes around the globe into a single array, and its first picture showed the black hole at the centre of the galaxy Messier 87.
Q 28Which colour do the very hottest stars shine, with surfaces several times hotter than the Sun's?
Blue
Blue stars of spectral class O have surfaces of 30,000 kelvin or more and pour out so much ultraviolet that they look bluish-white to the eye.
Q 29Which NASA telescope, carried up by Space Shuttle Columbia in 1999, studies black holes and exploded stars in X-rays?
Chandra
Chandra honours the astrophysicist Subrahmanyan Chandrasekhar, and the name also happens to mean "moon" in Sanskrit.
Q 30Which X-ray source, the first widely accepted black hole, did Stephen Hawking and Kip Thorne famously bet on?
Cygnus X-1
Cygnus X-1 was found in 1964 by instruments on a sounding rocket, and Hawking, who bet against a black hole while hoping to lose, conceded in 1990.