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Analog waves, digital pulses

Science · Waves, Light & Sound · ages 11-14

Name ______________________ Date ____________

Look at this pattern of pulses. Which type of signal does it show?
- A smooth analog wave
- A coded digital signal
- No signal at all
Which best describes an analog signal?
- It changes smoothly through every value in between
- It only uses two fixed values, on and off
- It is always sent by radio waves
True or false: before your voice can travel as digital pulses, a microphone must first measure it and turn it into numbers.
Circle one: True False
An analog radio wave and a digital radio wave both pick up static on a long trip. Which signal keeps its information intact?
- The analog signal, because waves are naturally noise-resistant
- The digital signal, because its on/off pulses can be cleaned up at each relay
- Neither: both lose their information equally
A digital pulse picks up a little noise as it travels down a cable. Why can the receiver still read it correctly?
- The receiver rounds the blurred pulse to the nearest 1 or 0 and cleans it up
- Noise never affects digital signals at all
- The receiver ignores every pulse that looks slightly wrong
When you speak into a phone, what happens to your voice first?
- It is turned straight into radio pulses with no analog step
- A microphone measures the analog sound wave and turns it into numbers
- It is stored as a photocopy of the sound
A digital photo copied and emailed around the world still looks identical to the original, but a photocopy of a photocopy gets blurrier each time. What protects the digital photo's information?
- Digital photos are physically smaller so there is less to blur
- Email servers automatically sharpen blurry images
- Each digital copy resends the exact same numbers, which can be checked and corrected
Zara says digital signals are just better because computers like them. What is the real reason digital signals resist noise better than analog ones?
- Digital signals never travel through noisy environments
- A 1-or-0 pulse can be told apart from noise and copied exactly, unlike a smooth analog value
- Digital signals are always louder than analog signals

Answer key

For grown-ups. Fold this page away before handing over the rest.

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A coded digital signal · A pattern of fixed on/off values like this is exactly what makes a signal digital, not analog.
It changes smoothly through every value in between · Analog signals vary continuously, taking any value in a range, not just fixed steps.
True · Digitising sound starts with measuring the analog wave many times per second and recording each measurement as a number.
The digital signal, because its on/off pulses can be cleaned up at each relay · Digital pulses can be detected, cleaned, and recopied exactly at each stage, so the message survives long trips better than a smooth analog wave.
The receiver rounds the blurred pulse to the nearest 1 or 0 and cleans it up · Because digital pulses only need to be told apart as a 1 or a 0, a receiver can round off small noise and recover the exact pulse.
A microphone measures the analog sound wave and turns it into numbers · The microphone first captures your voice as an analog wave, then measures it many times per second to create numbers.
Each digital copy resends the exact same numbers, which can be checked and corrected · A digital copy is just a set of numbers being resent exactly, so there is nothing to gradually blur the way a physical analog copy blurs.
A 1-or-0 pulse can be told apart from noise and copied exactly, unlike a smooth analog value · The real advantage is that discrete on/off values can be recognized and cleaned even after picking up some noise, while a continuous analog value cannot be separated from the noise added to it.