Digital and analog signals
Grade 8 Science Worksheet
Circle the best answer, or write your answer on the line.
Ari's recorder takes 2000 samples every second, and each sample is stored in 8 bits. How many bits does a 3-second recording need?
Bo's phone takes 1000 samples every second, and each sample is stored in 16 bits. How many bits does a 4-second clip need?
Esme's sensor takes 500 samples every second, and each sample is stored in 12 bits. How many bits does 6 seconds of readings need?
Bits sent: 1, 0, 0, 1, 1. Which pulse did the receiver misread, and why, Jun?
- The second, since 0.15 is not exactly 0
- No pulse, since digital signals are not misread
- The third, since noise raised a 0 to 0.62
- The fifth, since 0.85 is below a full pulse
Bits sent: 0, 1, 1, 0, 1. Which pulse did the receiver misread, and why, Kira?
- No pulse, since each one is close to what was sent
- The third, since noise lowered a 1 to 0.45
- The fifth, since 0.8 is too low
- The first, since 0.2 is not exactly 0
Bits sent: 1, 1, 0, 0, 1, 0. How many bits does the receiver read wrongly, Luz?
- One, the 0.4 reading alone
- Two, the second bit and the fourth bit
- Four, since four pulses are not exactly 0 or 1
- Zero, since digital signals ignore noise
Read this first
Lab report, Copying a recording (example data)
[1] Ren's class compared two ways of copying one recording. [2] They copied an analog tape, then copied that copy, and kept going until they had five generations. [3] They also copied a digital file five times in a row. [4] After each copy, they measured how far the result differed from the original. [5] The tape's difference grew with every generation: 2%, 4%, 7%, 11% and 16%. [6] The digital file's difference stayed at 0% for all five copies. [7] Noise explains the tape results, because each copy added small random changes that the next copy kept as part of its shape. [8] A digital receiver only decides whether each pulse is closer to 0 or to 1, so small changes were thrown away at every step. [9] The class noted that a very noisy cable could still make a receiver misread a pulse, which would flip a bit.
Which sentence explains why the digital copies stayed the same, Noah?
- Sentence 3
- Sentence 8
- Sentence 6
- Sentence 7
What does sentence 9 add that sentences 5 to 8 leave out, Pia?
- A sixth measurement of how the tape copies drifted
- A limit: strong enough noise can still flip a digital bit
- A reason to stop using digital files for recordings
- Proof that digital copies get steadily worse over time
Cable test (example data)
cable length (m) bits sent bits misread 10 10000 0 50 10000 2 100 10000 9 200 10000 38 Which conclusion does the cable table support best, Ren?
- A digital signal cannot be misread on any cable
- Cable length has no effect on how many errors happen
- Each bit sent on the 200 m cable was misread
- More misread bits on longer cables, yet most bits arrived
Bits per sample at 1000 samples per second (example data)
bits per sample brightness levels bits stored per second 2 4 2000 4 16 4000 8 256 8000 Going from 4 bits to 8 bits per sample, what changes in the table, Tala?
- Levels stay the same, but the storage needed doubles
- Levels go up 16 times, but storage only doubles
- Levels and storage both go up 16 times over
- Levels and storage both double when the bits double
