Teacher Answer Key: Frequency and Amplitude
Introduction to Mobile Robotics > Frequency and Amplitude Exploration
Exploration 1: Amplitude – Gather Data
Observations:
1. The sound value you got for each tone in the sequence (Record in data table on last page)
These answers will differ from student to students. See table on the last page for sample answers.
2. Based on what you heard, what changed about the sound between each successive tone?
What stayed the same?
Students should note that the tones increased in volume from the first to the last. They should also
notice that the note never changed.
Exploration 1: Amplitude – Analyze the data (1)
3. Plot the data from the four different tones in order using either a bar graph or a line graph,
underneath the data table on the last page of this worksheet.
Below are two different ways of plotting the same information. On the left is a bar chart, and on the right is
a line graph. Both use the sample numbers from the table on the last page.
If the data was taken accurately, it should produce an upward trend, like that shown below. The lower and
upper ends of the trend line will depend on the volume to which students set their speakers as well as
how far the Sound Sensor is from the speakers. This should be corrected by playing the test tone in Step
1 and setting the position of the robot so that it reads 25%. If more than one tone produces a reading of
100, have the group retake the data with the speaker volume turned down, or the Sound Sensor farther
away.
4. The four tones you heard in this Exploration all had the same sound frequency (and
wavelength), but had successively increasing sound amplitudes. Based on your pattern of
results …
i. Would you say that the Sound Sensor’s readings are affected by the amplitude of a
sound wave?
Yes. The sensors readings should have gone up with each successive tone. This is because the
amplitude (volume) of the tone increased.
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ii. If yes, then is there a clear pattern to the way in which the Sound Sensor values
changed based on the sound wave’s amplitude? Explain.
Yes, there is a clear pattern. As the volume of the tone increases, so do the readings. Because
we cannot measure the volume, we don’t know if this relationship is directly linear or not, but we
do know that they are directly related (rather than inversely related).
5. Summarize briefly your findings regarding the Sound Sensor and the amplitude of sound
waves.
As the tones increased in amplitude (volume), so did the Sound Sensor readings. This probably
means that the Sound Sensor can sense the volume of the sound fairly well, but we won’t know this for
sure until we do more research and testing.
Exploration 2: Frequency – Gather Data
Observations:
6. The sound value your got for each tone in the sequence (Record in data table on last page)
These answers will differ from student to students. See table on the last page for sample answers.
7. Based on what you heard, what changed about the sound between each successive tone?
What stayed the same?
Students should note that the tones are all different in pitch. Some are higher pitched, some are lower
pitched. But they are about the same volume every time.
Exploration 2: Frequency – Analyze the data (2)
8. Plot the data from the four different tones in order using either a bar graph or a line graph,
underneath the data table on the last page of this worksheet.
Below are two different ways of plotting the same information. On the left is a bar chart, and on the right is
a line graph. Both use the sample numbers from the table on the last page.
If the data was taken accurately, it should produce no visible trend, just a scattered assortment of points.
If students constantly read values of 100 off their NXTs, have them repeat the exploration with the volume
of the speaker turned down, or the Sound Sensor farther away.
9. The four tones you heard in this exploration all had the same sound amplitude, but had
successively increasing sound frequencies. Based on your pattern of results …
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i.
Would you say that the Sound Sensor’s readings are affected by the frequency of a
sound wave?
Yes, the readings are affected by the frequency. The data students should get will be random
and unrelated, showing no visible trend like the first exploration did. But the number will all be
different, showing that yes, the Sound Sensor is sensitive to changes in sound wave frequency.
ii. If yes, then is there a clear pattern to the way in which the Sound Sensor values
changed based on the sound wave’s frequency? Explain.
There is no clear pattern. The randomness of the data should lead students to believe that there
is no clear pattern. They may recognize a general upward trend, but it will not be as clear as the
trend in the first exploration, and may have happened by chance.
10. Summarize briefly your findings regarding the Sound Sensor and the frequency of sound
waves.
There is no way to predict the Sound Sensor reading based on the frequency of the sound, but the
Sound Sensor will recognize one frequency from another, if they are at the same amplitude. These
findings, however, could use some more testing for further verification.
Conclusions: Sound and Sound Sensor
Answer the following:
11. Which quality or qualities of a sound wave affect the value that the Sound Sensor displays?
The Sound Sensor can really be affected by the amplitude of a sound wave (how loud it is), but it
doesn’t follow any recognizable pattern in its readings when the frequency of the sound wave was
changed.
12. Write a short recommendation for or against the use of the Sound Sensor in each of the
following situations. Be sure to explain the reason(s) for your decision.
i.
Automatic noise-detecting light switch for the cafeteria staff (see Clap On, Clap Off
activity).
This is probably a good idea. The Sound Sensor is most sensitive to changes in volume, which
is really what you would want to measure in the school cafeteria, so it would be a plausible use
for it. However, there are other factors that might affect this. See Clap On, Clap Off Teacher’s
Guide for more information.
ii. Tuning device for string instruments in the school orchestra.
Not a good idea. The Sound Sensor can’t determine changes in pitch very well, so it wouldn’t
know if you were playing an A or and A flat.
iii. Voice recognition device (something that can tell the difference between people’s
voices) for a home security system.
Not a good idea. Differences in people’s voices are the same as differences in the pitch of the
sound that comes out of our mouths. The Sound Sensor doesn’t recognize differences in pitch
very well. Voice recognition software is very complicated and requires more sensitive equipment
than the LEGO Sound Sensor.
iv. Siren detector on traffic lights that listens for the siren of an approaching ambulance,
fire truck, or police car, and automatically turns the light green for them.
Yes, this would work, but it might not be the best idea. The Sound Sensor can detect
increases in volume (amplitude) well, so it could detect the siren getting nearer, and then change
the light. However, it can also be affected by other sounds, such as nearby construction or trucks
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passing by. Non-emergency drivers may figure out this system and use it to their advantage, to
the disadvantage of all the other drivers.
v. Tea kettle watcher that listens for the whistle of a boiling tea kettle and turns the
stove off.
This would work, and possibly be quite useful, especially if there’s nothing else going on
in the kitchen. The robot would easily detect the increase in volume when the tea kettle starts
whistling, unless there were other loud noises in the room.
vi. Baby monitor that alerts parents when a baby is crying in a crib at night.
Also a very possible product, as a baby’s room should be silent at night anyway, so that the
baby can sleep. Then, if the Sound Sensor detects any sound, the robot will alert the parents.
Either the baby has awoken, or something else is wrong.
13. Suggest one or two more experiments that could be done to further explore the behavior of
the Sound Sensor.
Try playing the same sound, but moving the sensor further away each time.
Try more frequencies, all at the same amplitude.
Try more amplitudes, all at the same frequency.
There are many other possibilities. Check to see that students are keeping some variables (battery level,
distance to speaker, amplitude, frequency, etc.) constant while varying another, as these are the marks of
a well thought out experimental procedure.
14. What is the term commonly used to describe the sound wave property of amplitude? What is
the term commonly used to describe frequency?
The amplitude of a sound wave is indicative of the volume of the sound.
The frequency of a sound wave generally describes the pitch of the sound.
This information is covered in the helper page that is link on the first page of this section.
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Tables: Frequency and Amplitude
Introduction to Mobile Robotics > Clap On, Clap Off > Continue Activity
Values in magenta are Sample Values.
Students’ values will differ depending on the volume at which the speaker is set, the distance
between the speaker and the Sound Sensor, and the amount of background noise.
Exploration 1: Amplitude
Sound
Sensor Value
1st Tone
25
2nd Tone
50
3rd Tone
75
4th Tone
100
3. Plot the data from the four different tones in order using either a bar graph or a line graph.
Exploration 2: Frequency
Sound
Sensor Value
1st Tone
25
2nd Tone
32
3rd Tone
21
4th Tone
28
1. Plot the data from the four different tones in order using either a bar graph or a line
graph.
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