WEBVTT

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This time, a wheel with 6 North in red, 6 South in green!

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We check the polarities :-)!

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The frequency meter (Hertz) and our central needle galvanometer

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And the digital oscilloscope. We put the disc in rotation ...

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Attention: 12 poles (6 pairs North / South) per turn; so 1 round = 6 periods!

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The coil is connected to the 3 measuring devices

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One observes a sinusoid and a frequency of about 1 Hz (0.927), note the beats of the needle!

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Also visible on the oscilloscope

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One accelerates, the inertia of the needle limits its displacement, the frequency has increased, the amplitude in tension too!

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6 tiles * 50 ms = 300 ms of period. Frequency f = 1 / 0.3 ms = 3.33 Hz! For 3.38 reads: almost perfect :-)

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It accelerates

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5 tiles * 20 ms = 100 ms for the period. Frequency = 1 / 0.1 s = 10 Hz as read!

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To differentiate period and frequency, I will cite my great grandfather electrician in production:

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He said: "We have 50 periods!" Hertz was not his word, but it's interesting: 50 period per second, so 1 period lasts 1 / 50th of a second!

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So here with 10 Hz only, 1 period lasts 100 ms or 0.1 seconds!

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By cons the needle no longer allows a safe count :-)!

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Frequency, amplitude and speed are proportional!

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Experiment: we check here that by dividing by 2 the speed, I divide by 2 frequency and voltage!

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E = Delta phi / Delta t; when t, the period decreases: the voltage A increases! And the frequency too!