Grade by Grade
C. Matter and Energy · Light and Sound

Our Eyes, Our Ears, and Devices That Use Light and Sound

C2.8 A2.1 A2.2 A3.1About 40 minutes
Learning goals
  • I can describe how my eyes use light and my ears use sound.
  • I can name devices that use light and devices that use sound, and say which property each one uses.
  • I can describe how some animals use sound to find their way.
  • I can read, test and debug code for an automatic night light.
  • I can name jobs that work with light and sound.

Words to know

sensory organ
A body part that senses the world. Your eyes sense light and your ears sense sound.
pupil
The dark opening in the middle of your eye that lets light in.
retina
The layer at the back of your eye that senses light.
eardrum
A thin layer inside your ear that vibrates when sound waves hit it.
echolocation
Finding things by making sounds and listening for the echoes, like bats do.
sensor
A device part that measures something, like light or sound, so a computer can use it.
debug
To find and fix a mistake in code.

Built-in detectors

You carry two amazing detectors with you everywhere: your eyes detect light, and your ears detect sound. They are sensory organs. People have also invented many devices that use light and sound to help us see, hear, talk and stay safe.

Binoculars, headphones, a magnifying glass, eyeglasses and a flashlight lying on a wooden table.
Each of these devices uses light or sound. Which ones help our eyes, and which one helps our ears? AI-generated image

How your eyes use light

  1. Light from an object enters your eye through the pupil, the dark hole in the middle. The coloured ring around it, the iris, makes the pupil bigger in dim light and smaller in bright light.
  2. The lens behind the pupil bends the light (refraction!) to make a clear picture.
  3. The picture lands on the retina at the back of your eye. The retina senses the light.
  4. The optic nerve sends messages from the retina to your brain, and your brain tells you what you see.
lightpupillensretinaoptic nerve
Light enters through the pupil. The lens bends it onto the retina. The optic nerve carries the message to the brain.

How your ears use sound

  1. Your outer ear is shaped like a scoop. It collects sound waves and funnels them into the ear canal.
  2. The sound waves make your eardrum vibrate.
  3. The eardrum passes the vibrations to three tiny bones in your middle ear, the smallest bones in your body.
  4. The vibrations reach the cochlea, a snail-shaped part filled with liquid. It changes vibrations into messages.
  5. A nerve carries the messages to your brain, and you hear the sound.

Take care of these organs: wear sunglasses in bright sun and on snow, never look at the Sun, keep sounds at safe levels, and never put anything into your ear canal.

outer earcollectseardrumvibrates3 tiny bonespass it oncochleamakes messagesnerveto the brainsound wave inHearing is a relay race of vibrations!
The path of a sound through your ear. The vibration is passed along from part to part until the nerve carries a message to your brain.

Animals use light and sound too

  • Bats hunt insects at night using echolocation. They make high-pitched sounds and listen for the echoes that bounce back from insects and trees.
  • Dolphins and beluga whales also use echolocation underwater.
  • Owls have large eyes for seeing in dim light, and very sharp hearing.
  • Cats have a mirror-like layer at the back of their eyes that reflects light, helping them see at night. That is why their eyes shine in headlights.
Just for fun

A bat hunting with echolocation is like playing hide-and-seek by shouting "Where are you?" and listening for the answer bouncing back. Except the bat's shout is so high-pitched that people can't hear it!

DeviceLight or sound?How it works
eyeglasses, magnifying glass, microscopelightlenses refract (bend) light
periscope, car mirrorslightmirrors reflect light
solar panellightabsorbs light energy and makes electricity
fibre-optic cablelightlight reflects along inside thin glass threads, carrying internet signals
microphonesoundvibrations are changed into electrical signals
speakersoundmakes a cone vibrate to make sound waves
hearing aidsoundmodifies sound: makes it louder
sonar on a shipsoundsends sound down and times the echo to find depth or fish
ultrasound at a hospitalsounduses echoes to make pictures of the inside of the body
Devices that use the properties of light and sound

Jobs with light and sound

  • An optometrist tests people's eyes and prescribes glasses.
  • An audiologist tests hearing and fits hearing aids.
  • An electrician (a skilled trade) installs and repairs lights and wiring in homes and buildings.
  • A sound technician sets up microphones and speakers for concerts and shows.
  • A lighting technician controls the lights for plays, concerts and films.
  • A photographer uses lenses and light to take pictures.

Coding with a light sensor

Many devices today have sensors and computer code. A light sensor measures how bright it is. Code can use that number to make decisions. Street lights, phone screens that dim in the dark, and automatic night lights all do this.

In this code, the light level goes from 0 (totally dark) to 100 (very bright).

when the program starts
forever
set brightness to (light sensor reading)
if brightness < 30 then
turn lamp ON
else
turn lamp OFF

Code for an automatic night light. The sign < means "is less than".

Worked example

Let's test and debug the night light

Rosa wrote her night light code, but she typed one line wrong:

  • if brightness > 30 then turn lamp ON
  • else turn lamp OFF

She tested it at noon (brightness 80) and at night (brightness 5).

  1. Test at noon: brightness is 80. Is 80 > 30? Yes, so the lamp turns ON. That is wrong: we don't need a night light at noon!
  2. Test at night: brightness is 5. Is 5 > 30? No, so the lamp turns OFF. Also wrong: it should be on in the dark.
  3. Find the bug: the sign is backwards. She used > (greater than) instead of < (less than).
  4. Fix: change it to if brightness < 30 then turn lamp ON.
  5. Test again: noon, 80 < 30? No → lamp OFF. Night, 5 < 30? Yes → lamp ON. It works!

The bug was the > sign. Changing it to < makes the lamp turn on only when it is dark.

Emerging technology

Light and sound sensors with code are everywhere now: automatic street lights, motion-sensor lights, smart speakers that listen for your voice, doorbells with cameras, and phones that can show the sound level around you. These help people save energy and stay safe, but people also ask good questions about privacy: who hears or sees what these devices record?

Hands-on activity

Senses and devices hunt

You need: a hand mirror, a flashlight, paper and a pencil.

Part 1: Watch your pupils. In a room with dim light, look at one eye in the mirror for 30 seconds. Then a grown-up turns on a bright ceiling light (don't shine a flashlight into your eye). Watch your pupil. What happens? Turn the light off again and watch.

Part 2: Cupped ears. Have someone talk quietly across the room. Cup your hands behind your ears. Does it sound louder? Your hands act like bigger outer ears, collecting more sound waves.

Part 3: Device hunt. Find at least 6 devices in your home that use light or sound (a smoke alarm, speakers, a phone camera, glasses, a doorbell, mirrors, a microwave beep...). Make a table: Device, Light or sound?, What does it do?

Part 4: Unplugged code. Act out the night light code. A grown-up says a brightness number from 0 to 100. If it is less than 30, you switch on a flashlight; otherwise, you switch it off. Then change the rule to "less than 50" and play again.

What to look for: the pupil gets smaller in bright light and bigger in dim light; cupping ears makes sounds louder; the device table names at least 6 devices with a correct light-or-sound label; in the code game, the flashlight goes on only for numbers below the rule number.

Safety: never shine a flashlight directly into eyes, and never put anything into your ears.

Your turn

1

Which sensory organ detects light? Which detects sound?

2

What part of the eye bends light to make a clear picture?

3

What part of the ear vibrates when sound waves hit it?

4

How does a bat find insects in the dark?

5

Name one device that uses light and one that uses sound.

6

Which job tests hearing and fits hearing aids?

7

In the night light code, if the brightness is 10, does the lamp turn on or off?

More practice: warm-up

1

What is the dark opening in the middle of your eye called?

2

Which part of the eye senses the light?

3

Does a speaker use light or sound?

4

Does a periscope use light or sound?

5

Which skilled trade installs lights and wiring in buildings?

More practice: on your own

1

Why does your pupil get smaller in bright light?

2

How do eyeglasses use a property of light?

3

How does sonar on a fishing boat find fish?

4

In the night light code, what happens when the brightness is exactly 30? Explain.

5

Rosa wants the lamp to turn on a little earlier in the evening, while it is still a bit bright. Should she change 30 to 20 or to 40? Why?

Challenge

1

Explain the path of sound from a friend's voice to your brain. Use at least four ear parts.

2

Write a line of code for a sound-level warning sign: it should show "Too loud!" when the sound level is above 85.

3

A smart speaker listens for its name all day. Give one way it helps people and one question people might worry about.

Check your understanding

Quiz

1.

Which part of the eye senses light and sends messages to the brain through the optic nerve?

2.

Sound waves make which part of the ear vibrate first?

3.

Bats find insects in the dark using...

4.

Which device uses lenses that bend light?

5.

Which device uses echoes of sound?

6.

In the code "if brightness < 30 then turn lamp ON", when does the lamp turn on?

7.

An optometrist is a person who...

For parents and teachers

Big idea: Ontario Grade 4 expectation C2.8 asks children to identify devices that make use of the properties of light and sound; the eyes and ears are included here as the body's own light and sound detectors. The eye (pupil, iris, lens, retina, optic nerve) and ear (outer ear, eardrum, tiny bones, cochlea, nerve) are described simply. The night-light code uses a sensor reading and an if/else decision, with testing and debugging (A2.1); the emerging-technology note (A2.2) and jobs list, including the skilled trade of electrician (A3.1), connect science to everyday life.

How to help: Next time you visit an optometrist or have a hearing test, ask the professional to show your child the equipment. Point out sensors: automatic doors, street lights that switch on at dusk, phone screens that dim.

Common difficulties:

  • Mixing up eye and ear parts. Pupil/lens/retina are eye; eardrum/cochlea are ear.
  • The < and > signs. The open side faces the bigger number: 5 < 30 means "5 is less than 30".
  • Thinking the code is wrong whenever it surprises them. Encourage testing with specific numbers, like Rosa did.

Coding note: no computer is needed; the unplugged game works well. If your child uses a block-coding app or a micro:bit, many have a real light sensor to try this with.

Safety: never shine lights into eyes; never put objects in ears.