Manual

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29. Sound Waves
Build the circuit, press the switch (62), then hold
the press switch (61). When you move the magnet
(7) towards the reed switch (83), you will hear the
alarm (78). If you move the magnet (7) away, the
alarm (78) will turn off. The alarm (78) makes sound
by creating sound waves, much like light waves,
but at much longer wavelengths and much lower
frequencies. Frequency is the inverse of wavelength
(Frequency = 1÷Wavelength) and is measured in
Hertz (Hz). The human ear can hear sound waves
between about 20 Hz and 20 kHz (20,000 Hz).
30. Motors and Magnetic Fields
Build the circuit, press the switch (62), then hold the press
switch (61). When you move the magnet (7) towards the
reed switch (83), you will see the motor (95) turn on. If
you move the magnet (7) away, the motor (95) will turn off.
Now put the magnet (7) near the motor (95). Note that
the magnet (7) is attracted to the motor (95) at certain
locations. This is because motors have magnets inside
them that create a magnetic eld. When a current ows
through this magnetic eld (the circuit is ON), it creates a
force (look up Fleming’s rule) that spins the motor shaft.