MS-PS4-3: Why Digitized Signals Are More Reliable Than Analog Signals
In plain English: MS-PS4-3 is the NGSS middle school performance expectation that asks students to combine qualitative scientific and technical information to support the claim that digitized signals are a more reliable way to encode and transmit information than analog signals. Students compare what noise does to each kind of signal in fiber optic cables, wifi and stored files. It is usually taught in grade 7 or 8 physical science.
Integrate qualitative scientific and technical information to support the claim that digitized signals are a more reliable way to encode and transmit information than analog signals.
Clarification Statement: Emphasis is on a basic understanding that waves can be used for communication purposes. Examples could include using fiber optic cable to transmit light pulses, radio wave pulses in wifi devices, and conversion of stored binary patterns to make sound or text on a computer screen.
Assessment Boundary: Assessment does not include binary counting. Assessment does not include the specific mechanism of any given device.
Next Generation Science Standards · Disciplinary Core Idea: Waves and Their Applications in Technologies for Information Transfer · Official standard
Students gather evidence for one claim: a digitized signal is a more reliable way to send and store information than an analog signal. A signal is anything that carries a message from one place to another, such as light in a cable or radio waves in the air. To encode information means to turn it into a signal, and to transmit it means to send it. In an analog signal, the level can be any value, and the level itself is the message, like the loudness of a voice from moment to moment. In a digitized signal, the message is turned into a pattern of just a few set levels, usually a pulse (a short burst of a wave, called on) and no pulse (off). Every signal picks up noise, small unwanted changes on the way. Noise becomes part of an analog message for good, but a receiver of a digitized signal only has to decide on or off, so small noise is thrown away. Students combine text, data tables and diagrams into a written argument, which is the practice of obtaining, evaluating and communicating information.
The NGSS Clarification Statement says: "Emphasis is on a basic understanding that waves can be used for communication purposes. Examples could include using fiber optic cable to transmit light pulses, radio wave pulses in wifi devices, and conversion of stored binary patterns to make sound or text on a computer screen." The Assessment Boundary says: "Assessment does not include binary counting. Assessment does not include the specific mechanism of any given device." So patterns on this page are written as on and off, and students never convert numbers into binary. Devices are described only by what they send and receive, not by how their parts work. All readings, counts and test results are invented for teaching and labeled as invented. The information cards are written for this page.
Learning Objectives
By the end of this lesson, students will be able to:
Describe the difference between an analog signal, whose level can be any value, and a digitized signal, a pattern of a few set levels such as on and off
Use a decision line to read a noisy digitized signal, and explain why small noise does not change the message
Explain why noise builds up when an analog signal is passed along or copied, while a digitized signal can be passed along or copied with no loss
Combine information from texts, data tables and diagrams about fiber optic cables, wifi and stored files into a claim, evidence and reasoning argument
State a limit of the claim: very large noise can still flip a pulse, so engineers keep levels far apart and add checks
Prior Knowledge Required
Students should already be comfortable with:
Using patterns, such as codes of flashes or drumbeats, to send information over a distance 4-PS4-3
Waves as repeating patterns with an amplitude (height) and a wavelength 4-PS4-1
Light and sound as waves that carry energy from place to place
Writing a claim supported by evidence and reasoning
Line up two rows of five students. Row 1 passes a whispered sentence down the line while the rest of the class talks quietly. Row 2 passes a pattern of six hand signals, each one either thumbs up or thumbs down, while the class does the same.
Warm-Up Prompt
"Both rows had the same noise around them. Which message arrived unchanged, and why? What is different about the two kinds of message?"
Compare the last person's version with the first in each row. Record ideas on the board. Students often notice that a thumb can only be up or down, so a person can copy it exactly, while a whispered word can be heard in many ways. Keep the list: the lesson names this idea "set levels".
Direct Instruction15-20 minutes
Two ways to encode a message. Define signal, analog signal, digitized signal, pulse and noise (see the overview). A receiver of a digitized signal uses a decision line, a level halfway between off and on: a reading above the line counts as on, and a reading below it counts as off. Use Diagram 1. In the top panel, noise changes the shape of the analog wave, and nothing tells the receiver which part is message and which part is noise. In the bottom panel, the pulses are just as noisy, but every reading lands clearly on one side of the decision line, so the pattern arrives exactly as sent. Work through the examples below. The first three are the official examples.
A fiber optic cable is a thin strand of glass that carries light. The sender switches the light on and off in a row of short time slots. At the far end, a light sensor gives these invented readings for 8 slots, where 1.0 is full brightness: 0.82, 0.10, 0.77, 0.85, 0.07, 0.12, 0.80, 0.09. The decision line is 0.5.
Result: Readings above 0.5 count as on and readings below it as off, so the receiver reads on, off, on, on, off, off, on, off. That is the pattern that was sent, even though no reading arrived at exactly 1.0 or exactly 0. The dimming and noise did not change the message.
Wifi: radio wave pulses (official example)
A wifi router sends information as short bursts (pulses) of radio waves. A microwave oven running in the next room adds noise. In one invented test, the noise raised off readings by up to 0.30 and lowered on readings by up to 0.25 (on = 1.0, off = 0).
Result: An off slot reads at most 0 + 0.30 = 0.30, and an on slot reads at least 1.0 - 0.25 = 0.75. Both stay on the correct side of the 0.5 decision line, so every pulse is read correctly. The message would only be at risk if the noise grew to 0.5, half the gap between off and on.
Stored pattern to text on a screen (official example)
A computer stores the letter A as a pattern of on and off squares in a grid 5 squares wide and 7 squares tall (Diagram 2). A screen lights the pixels (tiny squares of light) that the pattern marks as on. The file is copied from a laptop to a phone, from the phone to a tablet, and from the tablet to a second phone.
Result: Each copy only has to tell on from off for 35 squares, so the last copy holds the same pattern and the screen shows the same letter. Nothing fades from copy to copy. Sound works the same way: a stored pattern is turned back into a sound wave by the speaker.
An analog signal passed along a chain (contrast)
An analog level of 0.60 is sent through 3 relay stations. A relay station receives a weak signal and sends it on stronger, noise included. The invented noise added on the three legs of the trip is +0.04, -0.01 and +0.05.
Result: The level arrives as 0.60 + 0.04 - 0.01 + 0.05 = 0.68. The receiver cannot tell that 0.08 of it is noise, because 0.68 is also an allowed message. The error stays, and each new leg can add more.
When noise is too large (a limit of the claim)
On a very noisy line, an off slot (sent as 0) arrives reading 0.56, and an on slot (sent as 1.0) arrives reading 0.61. The decision line is 0.5.
Result: Both readings are above 0.5, so both are read as on, and the off slot becomes an error. Digitized signals stay exact only while the noise is smaller than half the gap between off and on. Engineers keep the levels far apart and send extra check pulses, so a receiver can notice a damaged part and have it sent again.
After each example, ask: "Where is the noise, and does it change the message?" Point out that pulses of light and radio are waves too: digitized information still travels as waves, only in a pattern of pulses.
Guided Practice15 minutes
Pairs analyze an invented relay test. The same message travels through 4 relay stations. On the analog line, each station sends on whatever level it received. On the digital line, each station reads the pulse with the 0.5 decision line and sends out a fresh, clean pulse.
Invented relay test: analog level sent as 0.40, digital on pulse sent as 1.00
Place
Analog level arriving
Digital reading arriving
Digital value sent on
Sender
0.40
1.00
on (1.00)
Station 1
0.45
0.84
on (1.00)
Station 2
0.43
0.91
on (1.00)
Station 3
0.50
0.79
on (1.00)
Station 4
0.54
0.88
on (1.00)
Find how far the analog level at Station 4 is from the level that was sent. (0.54 - 0.40 = 0.14 too high.)
Check each digital reading against the decision line. Is any reading below 0.5? What value does each station send on?
Why can't an analog station clean up the level the way a digital station does? (Hint: what is the "right" level for an analog message?)
Write one sentence that states the claim and cites a number from the table as evidence.
Independent Practice10-15 minutes
Each student reads two short information cards (written for this page) and writes a claim, evidence and reasoning paragraph that uses both cards and the Guided Practice table.
Card A, from a guide for cable installers: "Fiber lines send information as pulses of light. Over long distances the pulses grow dim and a little blurred. On long lines, stations along the way read each pulse as on or off and send out a fresh, bright copy."
Card B, from a radio history display: "Listeners to early AM radio heard crackles during thunderstorms. Lightning gives off radio waves, and that static mixed into the broadcast. The crackle became part of the sound, and no radio could take it back out."
A strong paragraph names which card describes a digitized signal and which describes an analog one, quotes or paraphrases one detail from each, cites a number from the table, and explains with the idea of set levels why noise is removed in one case and kept in the other.
Closure5 minutes
Exit ticket: "Which piece of evidence from today convinced you most that digitized signals are more reliable? Name where it came from (a text, a data table or a diagram) and explain how it supports the claim." Return to the warm-up list and label the thumbs signals "set levels" and the whisper "any level".
Teacher note: the Assessment Boundary leaves out binary counting and how any particular device works inside. If students ask how a phone turns radio pulses into a picture, say that the inside workings are beyond this standard; the claim here is only about why on-off patterns survive noise.
Differentiation Strategies
For Struggling Students
Give a printed number line from 0 to 1.0 with the decision line drawn at 0.5, so students can place each reading and see which side it falls on
Provide a sentence frame: "The claim is ___. One piece of evidence is ___ from ___. This shows ___ because a digitized signal ___."
Start with the hand-signal warm-up and the grid copying before any decimals appear
For Advanced Students
Ask students to find the largest noise a line can have before a pulse is misread, and explain why moving on and off farther apart helps
Have students find one weakness of digitized signals (for example, a pattern needs a device that can read it) and explain whether it affects reliability
Challenge: students design a simple check, such as sending each pattern twice, and explain how a receiver could use it to notice an error (beyond this standard)
Assessment Guidance
What to Look For
Check that students describe an analog signal as one whose level can be any value and a digitized signal as a pattern of a few set levels, not simply as "old" and "new". Look for arguments that cite specific evidence (a reading, a count, a detail from a card) and connect it to the reason: a receiver can only remove noise when it knows the few allowed levels. Listen for students who think digitized signals are not waves, and for students who claim digital signals can never have errors.
02
Classroom Activities
3 Activities
1
Pixel Picture Relay
25 minGroups of 6 (two chains of 3)
Each group runs two copying chains side by side. Chain A copies a curvy line drawing by tracing, each person tracing the copy made just before. Chain B copies a 10 × 10 grid picture square by square, each person shading every square that is shaded on the copy before. After 5 copies, groups compare the last copy with the original. The grid picture is a model of a stored pattern that a screen turns into an image.
Procedure
The teacher hands out the original drawing (one smooth curvy line across the page with 5 checkpoints marked on it) and the original grid picture (42 of the 100 squares shaded).
Chain A: each person lays tracing paper over the latest copy, traces the line in 2 minutes, and passes only the new copy on. Chain B: each person shades a blank 10 × 10 grid to match the latest copy, also in 2 minutes.
Take turns so that each chain has 5 copies. For the drawing, measure how far the line on each copy has moved from the original at the 5 checkpoints, in millimeters, and average them. For the grid, count the squares that differ from the original.
Sample Data (invented)
Chain A, average drift of the traced line from the original after copies 1-5: 0.8, 1.6, 2.2, 3.1, 4.0 mm. Chain B, squares that differ from the original after copies 1-5: 0, 0, 1, 1, 1. In Chain B, one copier left a square half shaded on copy 3, and the next copier read it as shaded.
Discussion Questions
The drift in Chain A grew after every copy. Why does each tracer add to the error instead of fixing it?
In Chain B, the one wrong square appeared on copy 3 and was copied forward, but no new errors joined it. Why did the error stay the same size instead of growing?
The half-shaded square acted like noise near the decision line. What rule could the class agree on to make copies even more reliable?
Which chain is a better model of copying a music file, and which is a better model of copying a cassette tape?
Modification for Distance Learning
Students copy on screen: chain A redraws a line with a drawing app from a photo of the last copy, and chain B fills in a shared spreadsheet grid. Post both chains' last copies side by side.
2
Rope Pulse Signals on a Noisy Line
20 minGroups of 4
A long jump rope (or a spring toy) is laid along the floor between a sender and a receiver. Side-to-side wave pulses travel along it. Groups send a message two ways: as pulses of different heights (analog) and as pulse or no pulse on each beat (digitized). A third student adds noise by gently jiggling the middle of the rope.
Procedure
Stretch the rope about 5 m along the floor in a clear space (stretch a spring toy only as far as it goes without staying stretched out, often 2-3 m). The sender holds one end, the receiver kneels at the other end beside a meter stick laid flat on the floor across the rope, and a noise maker sits at the middle. A recorder writes everything down.
Analog round: the sender sends 10 single pulses, each a side-to-side pulse whose height, from 10 to 40 cm, the recorder secretly chose. The receiver estimates each height against the meter stick as it arrives. Count a reading as correct if it is within 5 cm. Do this once with a still rope and once while the noise maker jiggles the middle with small, random shakes.
Digitized round: a metronome app or a hand drum gives a steady beat. On each of 10 beats, the sender either sends one pulse (on) or keeps still (off), following a pattern the recorder chose. The receiver writes on or off for each beat. Again, do it with and without noise.
Safety: keep the rope on the floor and send every pulse side to side along it, use small, controlled motions, never whip or swing the rope, never let go of a stretched spring (walk the ends together first), and keep other students at least 1 m away.
Sample Data (invented)
Analog round: 8 of 10 heights correct with a still rope, 4 of 10 with noise. Digitized round: 10 of 10 beats correct with a still rope, 9 of 10 with noise; the one error was a strong shake that the receiver mistook for a pulse.
Discussion Questions
Find the percent correct in each of the four trials. Which kind of message lost more when the noise was added?
Why is it harder to judge a pulse height than to judge whether a pulse arrived at all?
What kind of shake from the noise maker could still fool the receiver in the digitized round? How could the sender make that less likely?
Challenge Variation
Groups agree to send every beat of the pattern twice. They test whether the receiver can now notice the strong-shake error, and they explain what the extra pulses cost (time).
3
Evidence Stations: Building the Argument
25 minGroups of 3-4
Four stations each hold a short information card written for this page and one small table or picture. At each station, groups fill one row of an evidence organizer: the evidence, where it came from (text, data or diagram), and whether it supports or limits the claim. Groups rotate every 5 minutes and finish by writing one argument that uses at least three stations.
Station Cards
Station 1, fiber optic cable: "A school's internet connection arrives as pulses of light in a glass strand. The light dims along the way, but each pulse still reads clearly as on or off." Invented table: pulses sent in one test 2,000; pulses read correctly 2,000.
Station 2, wifi: "A wifi router sends radio wave pulses. Walls weaken them, and a running microwave oven adds noise. When a part of a message arrives damaged, the receiver notices and asks for that part again." Invented table: parts of a message sent 400; parts damaged by noise and sent again 6; parts wrong in the final message 0.
Station 3, stored patterns to screen and sound: a printed grid showing the letter B as on and off squares, and the card: "A song file is a stored pattern. The speaker turns the pattern back into a sound wave." Invented check: the file was copied 20 times, each copy made from the last, and the 20th copy was compared with the original part by part; differences found: 0.
Station 4, analog examples: "A cassette tape copied from another tape picks up a soft hiss. Copy it again, and the hiss grows. A photocopy of a photocopy gets blurrier each time." Invented table: a 120-word paragraph photocopied 4 times, each copy made from the last; readable words 120, 116, 108, 95.
Discussion Questions
At Station 2, some parts of the message were damaged, yet the final message had no errors. Does this support the claim, limit it, or both?
At Station 4, between which two copies were the most words lost? What does that suggest about copying analog information many times?
Which station gave the strongest evidence, and which gave evidence that is only a description? Explain the difference.
Modification for Distance Learning
Post each station as a slide. Groups work in breakout rooms, fill a shared evidence organizer, and post their argument to the class board.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: Noise on an Analog Signal and on a Digitized Signal
Top: an analog wave as it was sent (dashed) and as it arrives with noise added (solid). Every level is allowed, so the receiver cannot tell the noise from the message. Bottom: a digitized signal of 8 pulse slots with the same kind of noise. Each invented reading lands clearly above or below the decision line at 0.5, so the receiver reads on, on, off, on, off, off, on, on, exactly the pattern that was sent.
Diagram 2: A Stored On-Off Pattern Becomes a Letter on a Screen
Left: the letter A stored as a 5 by 7 pattern of on (dark) and off (light) squares. Middle: the pattern as read from a copy, where small noise makes the shades vary. Every square is still clearly dark or light, so the reader recovers the exact pattern. Right: the screen lights the pixels marked on and shows the same letter, no matter how many copies came before.
04
Homework Assignment
~30 min
MS-PS4-3 Homework: Evidence for Reliable Signals
Directions: All readings and test results are invented for practice. On = 1.0, off = 0, and every decision line is at 0.5 unless the problem says otherwise. End each problem with a sentence that says how your answer connects to the claim that digitized signals are more reliable than analog signals.
Part 1: Reading Signals Through Noise (Problems 1-2)
A light pulse pattern of 10 slots was sent as on, off, off, on, on, off, on, off, on, off. The readings at the far end are 0.91, 0.12, 0.08, 0.76, 0.83, 0.21, 0.69, 0.05, 0.88 and 0.30. (a) Write the pattern the receiver reads. (b) Does it match the pattern sent? (c) The largest reading in an off slot is 0.30. How much more noise could that slot take before it would be misread?
An analog sound level of 0.70 is sent through 4 relay stations. The invented noise on the four legs is +0.03, -0.02, +0.05 and +0.04. (a) Find the level after each leg. (b) How far is the final level from the level sent? (c) Station 4 receives the signal. Could it remove the noise? Explain.
Part 2: Copying and Storing (Problems 3-4)
A class tested copying a 120-word paragraph. Photocopies, each made from the last: readable words 120, 118, 111, 99 and 84 for copies 1-5. Digital file copies, each made from the last: 120 readable words on every copy. (a) How many words did the photocopies lose from copy 1 to copy 5? (b) Between which two copies were the most words lost? (c) Explain the difference between the two kinds of copies using the idea of set levels.
A letter is stored in a grid 5 squares wide and 7 tall. Row by row, the on squares are: row 1, all five; rows 2 and 3, only the first; row 4, the first four; rows 5 and 6, only the first; row 7, all five. (a) Shade the grid and name the letter. (b) The file is copied 50 times, each copy made from the last, with no reading errors. Describe the letter shown by copy 50. (c) Why would an analog picture of the same letter, copied 50 times, look different?
Part 3: Building and Testing Arguments (Problems 5-6)
Read two sources. Source 1 (text written for this page): "Pictures on old analog TV sets turned snowy and showed faint double images when the station was far away, and the picture flickered whenever a truck drove past the antenna." Source 2 (invented data): a school's digital radio link sent 500 messages on a quiet day and 500 while a large motor next to it was running. All 500 arrived correct on the quiet day. With the motor running, 3 arrived damaged, were noticed by the receiver and were sent again, so all 500 ended up correct. Write a claim, evidence and reasoning paragraph that uses both sources.
A classmate says: "Digital signals never have errors." A pattern was sent as on, off, off, on, off, on, and the readings were 0.71, 0.62, 0.15, 0.80, 0.33 and 0.66. (a) Read the pattern and find any slot that was misread. (b) How large was the noise in that slot? (c) Rewrite the classmate's claim so that it matches the evidence.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Reading the Signals
Every reading placed correctly against the decision line; analog levels added correctly
One reading misplaced or one addition error
Using Evidence
Cites specific numbers or details from each source or table and says where they came from
Evidence is general ("digital is better") or from one source only
Reasoning
Explains with set levels why noise is removed from digitized signals and kept in analog ones, and states a limit where asked
Reasoning is stated but does not connect the evidence to the claim
05
Quiz: 20 Questions
Interactive, with answers
Instructions
All readings and test results are invented. On = 1.0, off = 0, and the decision line is 0.5 unless a question says otherwise. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again. Short-answer questions show a model answer.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
Which description fits an analog signal?
Answer: C
In an analog signal, any level is allowed, and the level itself carries the message. Choice A describes a digitized signal. Choice B describes the pulses in a fiber optic cable, which are digitized, and choice D describes a stored digital pattern.
Question 2 of 20 · Multiple Choice
A song is stored as a digitized signal. What does that mean?
Answer: B
Digitizing turns the sound into a pattern of a few set levels, such as on and off. Choice C describes a record groove, which is an analog copy of the wave's shape. Loudness (choice A) has nothing to do with how the song is encoded.
Question 3 of 20 · Multiple Choice
Six light pulse slots arrive with the readings 0.12, 0.88, 0.09, 0.74, 0.35 and 0.93. The decision line is 0.5. Which pattern does the receiver read?
Answer: D
Readings above 0.5 are on and readings below it are off, so 0.35 is off and 0.74 is on. Choice A reads 0.35 as on, as if the line were at 0.3. Choice B flips every slot. Choice C reads 0.74 as off, as if the line were at 0.8.
Question 4 of 20 · Multiple Choice
Why can a receiver remove small noise from a digitized signal but not from an analog signal?
Answer: A
A digitized receiver knows the only allowed levels, so it can replace a noisy reading with the nearest allowed level. An analog receiver has no list of allowed levels. Choice B is false: both kinds of signal travel as waves, at the same speed in the same material, and speed does not protect a signal from noise. Choice C is false, since radio picks up noise too. Choice D is false because noise is added all along the way.
Question 5 of 20 · Multiple Choice
An analog level of 0.50 passes through 4 relay legs. The invented noise on the legs is +0.03, +0.02, -0.01 and +0.04. What level arrives?
Answer: B
0.50 + 0.03 + 0.02 - 0.01 + 0.04 = 0.58. Choice A assumes the relays remove noise, which analog relays cannot do. Choice C adds 0.01 instead of subtracting it. Choice D uses only the noise from the last leg.
Question 6 of 20 · Multiple Choice
A photo's sharpness is scored 100 on the original. It is copied 4 times, each copy made from the last. Which list of scores for copies 1-4 fits a digital file?
Answer: C
A digital copy holds the exact same pattern as the file it came from, so every copy scores the same. Choice A is what analog copying looks like: each copy adds a little noise. Copies never get sharper than the original (choice B), and choice D wrongly assumes each copy keeps only half.
Question 7 of 20 · Multiple Choice
Light pulses reach the far end of a long fiber optic cable much dimmer than they were sent, but the message still arrives correctly. Why?
Answer: A
The receiver only has to tell on from off, so a dim pulse that is still well above the decision line is read as on, and the pattern survives. Choice C contradicts the question: the pulses did grow dimmer. Choice B is wrong because the fiber carries a digitized pattern, and choice D would not give a reliable message at all.
Question 8 of 20 · Multiple Choice
Wifi pulses (on = 1.0, off = 0) pass through two classroom walls. On pulses arrive reading between 0.80 and 0.90, and off slots arrive reading between 0 and 0.15. The decision line is 0.5. What happens to the message?
Answer: D
The lowest on reading, 0.80, is above 0.5, and the highest off reading, 0.15, is below it, so every slot lands on the correct side of the decision line and the receiver rebuilds the exact pattern. Choice A confuses a reading of 0.15 with an error rate of 15%. Choice C treats the signal as analog, where the weakening would stay in the message.
Question 9 of 20 · Multiple Choice
The letter A is stored as an on-off pattern and copied from one phone to another. On the second phone, the letter shows with exactly one pixel wrong, and every other pixel matches. Which explanation best fits this evidence?
Answer: B
A single wrong square with every other square exact is what a digitized copy looks like when one reading lands on the wrong side of the decision line: the error is limited to that square. Choice A describes analog copying, where the whole picture would change a little. Choices C and D do not fit the evidence: the letter fits on the screen, and every other pixel matches the original.
Question 10 of 20 · Multiple Choice
The decision line is 0.5. Which reading from a slot that was sent as off would be misread?
Answer: C
Only 0.57 is above the decision line, so only that off slot is read as on. 0.46 (choice D) is close to the line but still below it, so it is read correctly as off. Choices A and B are well below the line.
Question 11 of 20 · Multiple Choice
Which piece of information best supports the claim that digitized signals are more reliable than analog signals?
Answer: A
Reliability means the message arrives or survives unchanged, and an exact match after 100 copies is direct evidence of that. Choices B and D are about sales and size, not reliability. Choice C is true but only describes how an analog record stores sound; it says nothing about how well it survives copying.
Question 12 of 20 · Multiple Choice
An invented test sent 50 words over a noisy cable. Analog: 48 words understood at 1 km, 39 at 5 km and 27 at 10 km. Digitized, with stations that send fresh pulses: 50, 50 and 50. Which conclusion do the data support?
Answer: D
The digitized message stayed at 50 of 50 at every distance, while the analog message fell from 48 to 27. Choice A is false because 48 is less than 50. Choice B ignores that the digitized signal lost no words, and choice C ignores the analog losses.
Question 13 of 20 · Multiple Choice
An analog receiver gets a reading of 0.72. What can it conclude about the level that was sent?
Answer: B
In an analog signal, any level is a possible message, so 0.72 could be the message or the message plus noise. Choice A ignores noise. Choice C applies the digitized decision rule to an analog signal, which has no set levels to choose from.
Question 14 of 20 · Multiple Choice
Which reasoning sentence best connects the evidence to the claim?
Answer: C
Good reasoning explains why the evidence supports the claim: set levels let a receiver throw small noise away. Choice B is a misconception, since pulses of light and radio are waves and they do pick up noise. Choices A and D give opinions about age and popularity, not a scientific reason.
Question 15 of 20 · Short Answer
A level of 0.40 is sent on an analog line, and the first relay station receives 0.47. An on pulse is sent on a digital line, and its first station receives a reading of 0.76. What does each station send on to the next leg, and which line keeps its noise?
The analog station sends on 0.47: it cannot tell that 0.07 of it is noise, so the noise travels on with the message. The digital station reads 0.76 as on (above 0.5) and sends on a full on pulse of 1.0, so the noise from the first leg is thrown away. The analog line keeps its noise.
Question 16 of 20 · Short Answer
A pattern was sent as on, off, on, off, off, on, on. The readings are 0.79, 0.27, 0.66, 0.53, 0.18, 0.84 and 0.47, and the decision line is 0.5. Which slots are misread? What does that tell you about the noise on this line?
The receiver reads on, off, on, on, off, on, off. Slot 4 (sent off, read on at 0.53) and slot 7 (sent on, read off at 0.47) are misread. In both slots the noise was more than 0.5, half the gap between off and on, so this line is too noisy for this decision line. The levels need to be farther apart, the noise needs to be reduced, or check pulses are needed so the damaged parts can be sent again.
Question 17 of 20 · Short Answer
Source 1 (written for this page): "A phone call on a digital network sounds the same whether the other person is across town or across the country." Source 2 (invented data): on an old analog phone line, listeners understood 47 of 50 test words over 2 km and 31 of 50 over 40 km. Use both sources to support the claim that digitized signals are more reliable.
Claim: digitized signals send information more reliably than analog signals. Evidence: the analog line lost words with distance, falling from 47 to 31 of 50 (Source 2), while digital calls sound the same at any distance (Source 1). Reasoning: noise builds up along an analog line and stays in the message, but on a digital network each part of the trip reads the on-off pattern and sends it on fresh, so distance does not pile up noise.
Question 18 of 20 · Short Answer
A cassette tape copied tape to tape 4 times gets more hiss with each copy, while a music file copied 4 times does not. Explain the difference using the idea of set levels.
The tape stores sound as an analog signal, where any level is allowed. Each copy records the hiss along with the music, and the next copy adds more hiss on top. The file stores a digitized pattern of set levels, so each copy only has to tell which level each part is. Small noise cannot change those choices, and the pattern, and therefore the sound, is copied exactly.
Question 19 of 20 · Short Answer
On a noisy line, off slots (sent as 0) arrive reading as high as 0.55, and on pulses (sent as 1.0) arrive reading as low as 0.60, with the decision line at 0.5. An engineer suggests sending on pulses at 2.0 instead of 1.0 and moving the decision line to 1.0. The noise stays the same. Will this fix the errors? Explain.
Yes. With the old levels, off slots that read up to 0.55 are misread as on. The noise lowers on pulses by up to 1.0 - 0.60 = 0.40, so with on = 2.0 they would arrive at at least 1.60, and off slots would still arrive at at most 0.55. Both stay on the correct side of the new decision line at 1.0. Moving the levels farther apart makes the gap larger than the noise, so the pattern is read correctly again.
Question 20 of 20 · Short Answer
A song is stored as a digitized pattern on a tablet. When it plays through an old speaker with a loose wire, the sound crackles. A student says the song file must be damaged. Use what you know about stored patterns to respond.
The crackle does not show that the file is damaged. The stored pattern is turned back into a sound wave at the speaker, and the noise is added after that, in the speaker and its wire. The pattern itself is still exact: playing the same file through a working speaker, or copying it to another device, would give the same clean song.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does MS-PS4-3 mean?
MS-PS4-3 asks students to use several kinds of information to support the claim that digitized signals send and store information more reliably than analog signals. Students read short texts, data tables and diagrams, and combine them into one argument. The code means Middle School, Physical Science, core idea 4 (Waves and Their Applications in Technologies for Information Transfer), performance expectation 3.
What grade is MS-PS4-3 taught in?
It is a grades 6-8 standard. Many schools teach it in grade 7 or 8, in a waves unit after students have described wave amplitude and how waves are reflected, absorbed or transmitted (MS-PS4-1 and MS-PS4-2).
What is the assessment boundary for MS-PS4-3?
Assessment leaves out binary counting and the specific mechanism of any given device. Students can describe a message as a pattern of on and off pulses, but they are not asked to convert numbers into binary. They can say that wifi sends radio wave pulses, but not how a router's circuits work.
What is the difference between an analog and a digital signal?
An analog signal can take any level, and the level itself is the message; a digital (digitized) signal turns the message into a pattern of a few set levels, usually on and off. A record groove shaped like the sound wave is analog. A song file stored as a pattern is digital.
Why are digital signals more reliable than analog signals?
Because a receiver of a digital signal only has to decide between a few set levels, so small noise does not change the message. With an analog signal, any change is a possible message, so noise stays in for good and builds up each time the signal is passed along or copied.
Do students need to learn binary numbers for MS-PS4-3?
No. The Assessment Boundary says assessment does not include binary counting. The clarification mentions "stored binary patterns", which on this page are shown as on and off squares or pulses. Converting numbers to binary can be an enrichment activity, but it is beyond this standard.
Can a digital signal still have errors?
Yes. If the noise is larger than half the gap between off and on, a pulse is misread. Digital systems reduce this risk by keeping the levels far apart, sending fresh pulses along the way, and adding check information so a damaged part can be noticed and sent again. A good student argument mentions this limit.
What does "integrate qualitative scientific and technical information" mean?
It means combining information from different kinds of sources, such as a short article, a data table, a diagram and a demonstration, into one explanation. Qualitative means the argument rests on descriptions and comparisons, not on detailed calculations. The small numbers on this page are counts and readings that students compare, not formulas.
What are good classroom examples for MS-PS4-3?
The Clarification Statement names light pulses in fiber optic cable, radio wave pulses in wifi devices, and stored patterns turned into sound or text on a screen. Low-cost models include copying a grid picture versus tracing a drawing, sending rope pulses past a noisy middle, and comparing photocopies of photocopies with copied files.
How does MS-PS4-3 connect to other standards?
It builds on 4-PS4-3, where students compare ways to send information with patterns. In high school, HS-PS4-2 asks students to evaluate questions about the advantages of digital transmission and storage, and HS-PS4-5 asks how devices use waves to send and capture information. Reading several sources and comparing them also practices RST.6-8.9.
07
Related Standards
6 standards
These standards connect to MS-PS4-3: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
4-PS4-3Prerequisite
Generate and compare multiple solutions that use patterns to transfer information
Lesson coming soon
Alongside
MS-PS4-1Parallel
Use a simple model of waves to relate a wave's amplitude to the energy it carries
NGSS is a registered trademark of WestEd. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.
