Manual

Turn on the slide switch (S1). The color LED (D8) is dim but the white
LED (D6) is bright.
Remove either LED (D6 or D8) and see what happens to the other one.
Project 99
The NPN transistor (Q2) is a current amplifier. When
a small current flows into Q2 through the left branch
(through D8), a larger current will flow into Q2 through
the right branch (with D6). Green arrows shown the
current flow. So the LED on the right side will be
brighter than the LED on the left side. The current in
the right branch might be 100 times larger than in the
left branch.
The left branch controls the right branch, so removing
D8 turns off D6, but removing D6 does not affect D8.
Use the preceding circuit, but swap the locations of the white LED (D6)
and the color LED (D8).
Project 100
Another Transistor Amplifier
Use either of the two preceding circuits, but replace either of the LEDs
(D6 or D8) with the horn (W1).
Notice how the horn makes little or no sound
when placed in the left branch (because the
5.1kW resistor is in series with it), but you
know that a small current is flowing through it
because the LED in the right branch is on.
Turn on the slide switch (S1). The color LED (D8) is blinking, the white LED
(D6) is on whenever the color LED is off, and the horn (W1) is making lots
of noise.
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Transistor Amplifier
Project 101
Transistor Amplifier w/ Horn
Project 102
Alternating Lights Sound
When the color LED is
off, the NPN transistor
(Q2) is off (and does not
affect the circuit), so
electricity just flows
through the horn and
white LED. When the
color LED is on, the
transistor is on and all the
electricity flowing through
the horn also flows
through the transistor,
bypassing the white LED
(turning it off).