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## High school physics

### Course: High school physics>Unit 12

Lesson 5: Discovery of resistors

# Listen to variable resistance

Here we draw a line on a page and use it as a variable resistor in series with a speaker. What relationship do we hear? Does it sound linear? Created by Brit Cruise.

## Want to join the conversation?

• What kind of paper was that? Where did you get the speaker?
I'm interested in doing this experiment/observation myself.
• This is just regular paper & pencil. The speaker is a Piezo buzzer which you can get at radio shack type stores for cheap.

Although soon I'll have DIY speakers! (see here for great project: http://www.youtube.com/watch?feature=player_embedded&v=R7zjfaPKMSE)
• Brit is using DC so how is the speaker produce sound? A speaker requires the input that is changing with some frequency.
• Apparently Brit is using Piezo Buzzer with built-in oscillator, which runs from DC.
Its loudness is determined by the DC voltage.
• When he rubbed the line with the wire,why did it make a squeaky sound?
• Because the wire was conducting electricity through the speaker, so the more electricity that got through, the more noise it made, the less electricity that got through the less noise it made. As for the line, well the line was graphite, which is a conductor, and as he brought the leads closer or farther apart, more or less electricity could get through.
• it that quiet and loud or high frequentie and lower frequentie?
(1 vote)
• What would happen if you simply drew a singular line across the page (one stroke across?)
(1 vote)
• As you need the graphite to conduct, and I don't believe paper can conduct anything, if you drew one thing singular line, you would probably get very little to no noise at all.
(1 vote)
• Does the sound come from the clip touching the pencil lead I am unclear.?
(1 vote)
• No, it comes from the electricity passing through the speaker.
(1 vote)
• what do the sounds mean, or do they not mean anything?
(1 vote)
• Brit was able to adjust the sound intensity by changing the location of an electrode. From this we see that he has made a variable resistor, which offers high resistance, low resistance, and a virtually unlimited set of intermediate resistances. Brit showed us how to make a variable resistor. He also helped us to develop intuition for variable resistors. If we curl, spiral, or helix the paper, then we have a compact version of a very long sheet of penciled paper.
(1 vote)
• does current passes through rocks
(1 vote)

Depends on the rock:

Iron, copper, and lead bearing rocks such as magnetite, hematite, galena, pyrite, chalcopyrite are conductors or at least "semiconductor."

Mica is an example of a good insulator. See https://en.wikipedia.org/wiki/Mica

Regards,

APD
(1 vote)
• What would happen if he drew a circle? When would the sound be high pitched and when will it be low pitched?