Data Sheet

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102. Sound Waves

Build the circuit shown, press and release the press switch (61) several

times and you will hear some clicks and pops from the speaker (93).

In order to translate an electrical signal into an audible sound, speakers

contain electromagnets made from a metal coil that creates a magnetic

eld when an electric current ows through it. The coil is designed such

that reversing the direction of the current in the coil ips the polarity

of the magnet. Inside a speaker, an electromagnet is placed in front of

a permanent magnet. The permanent magnet is mounted rmly while

the electromagnet can move. As pulses of electricity pass through the

coil of the electromagnet, the direction of the magnetic eld generated

is rapidly changed. This makes it repel from the permanent magnet,

vibrating back and forth. The electromagnet is attached to a cone made

of a exible material such as paper or plastic which amplies these

vibrations, pumping sound waves into the surrounding air and towards

your ears.

103. The Capacitor

In this circuit, we are going to learn how to charge and discharge a

capacitor. Build the circuit shown on the left. To charge the 470mF

capacitor (74), press & hold the press switch (61) and you will see the

star LED (70) turn on briey and fade out (you should be in a very dark

room to see these effects).

Capacitors come in all shapes and sizes, but usually have the same

basic components: two conductors (known as plates) and an insulator

in between them (called the dielectric). The two plates inside a capacitor

are wired to two electrical connections to the outside. When you connect

these wires to the battery, the plates in the 470mF capacitor (74) build

up charge. This charge is typical held by the capacitor until it is inserted

in a circuit where it can be discharged. When you see the star LED (70)

fade out then the 470mF capacitor (74) is near full charge. Release the

press switch (61) to disconnect the circuit. To discharge the 470mF

capacitor (74), touch the reed switch (83) with the magnet (7), and you

will see the heart LED (69) turn on briey and fade out, at which point

the 470mF capacitor (74) is near fully discharged.

2nd level

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