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Light & Sound: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
The Speed of Light
Light is the fastest thing there is: about 300,000 km every second. It could circle the Earth about 7.5 times in one second.
Key fact
Nothing with mass can reach the speed of light.
Electromagnetic Waves
Light is one kind of electromagnetic wave. Radio waves, microwaves, X-rays and visible light are the same kind of wave, with different wavelengths.
Key fact
Electromagnetic waves can travel through empty space.
Colours of Light
White light is a mix of colours. A prism or raindrops split it into a spectrum: red, orange, yellow, green, blue, indigo and violet.
Key fact
A rainbow is sunlight split by raindrops.
Sound Waves
Sound is a vibration that travels as a wave through air, water or solids. In air it moves at about 343 metres per second.
Key fact
Sound can’t travel through the vacuum of space.
Reflection & Refraction
Light bounces off mirrors, which is reflection, and bends as it passes from one material to another, which is refraction. That’s why a straw looks bent in water.
Key fact
Lenses in glasses and cameras use refraction to focus light.
Pitch & Volume
Pitch depends on how fast something vibrates: faster means higher. Volume depends on how big the vibrations are, and is measured in decibels.
Key fact
Human hearing spans about 20 to 20,000 vibrations a second.
Echoes & Sonar
An echo is sound bouncing back. Bats, dolphins and ships’ sonar send out sounds and listen for echoes to find things.
Key fact
Bats can catch insects in total darkness using echoes.
Fun facts
Moonlight is about 1.3 seconds old when it reaches your eyes.
Microwave ovens and Wi-Fi use similar wavelengths, about 12 cm long.
Seen from a plane, a rainbow can be a full circle. From the ground, the horizon hides the bottom half.
Count the seconds between lightning and thunder, then divide by three, to get the distance in kilometres.
Mirages happen when hot air near the ground bends light, making the sky look like water on the road.
Blue whale calls can reach around 188 decibels, louder than a jet engine.
Some blind people learn to echolocate, clicking their tongues and listening for the echoes.
Story: The Moon That Ran Late
The Moon That Ran Late
1676, Paris. Astronomer Ole Rømer times Io, one of Jupiter’s moons, as it slips in and out of the planet’s shadow.
Strangely, Io seems to run late when Earth is far from Jupiter, and early when Earth is near.
Rømer realised light takes time to cross the extra distance. For the first time, someone had shown light isn’t instant.
True or false?
Tap your answer to see if you got it, and why.
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Question 1 of 10
Light travels faster than sound.
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True. Much faster: that’s why you see lightning before you hear thunder.
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Question 2 of 10
Visible light is one part of the electromagnetic spectrum.
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True. A small slice between infrared and ultraviolet.
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Question 3 of 10
White light is made of many colours mixed together.
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True. A prism spreads them out.
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Question 4 of 10
Sound travels faster in water than in air.
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True. About four times faster.
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Question 5 of 10
A straw looks bent in water because light refracts.
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True. Light changes direction as it leaves the water.
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Question 6 of 10
Faster vibrations make a higher pitch.
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True. A short guitar string vibrates faster and sounds higher.
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Question 7 of 10
Some bats find their food using echoes.
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True. It’s called echolocation.
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Question 8 of 10
Light takes several hours to cross the Atlantic.
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False. It crosses it in about a sixtieth of a second.
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Question 9 of 10
Light needs air to travel through.
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False. It crosses the vacuum of space from the Sun to us.
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Question 10 of 10
You see a rainbow when you face the Sun.
Show the answer
False. The Sun has to be behind you.
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