Elenco LIGHT - Manual (Page 70)

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Project 150 Transistor
Project 151 Another Transistor
Build the circuit and turn on the slide switch (S1). Slowly move the lever
on the adjustable resistor (RV) across its range while watching the
brightness of the red & white LEDs (D1 & D6).
This circuit is just like the preceding one,
except uses a different type of transistor.
Build the circuit and turn on the slide
switch (S1). Slowly move the lever on the
adjustable resistor (RV) across its range
while watching the brightness of the red
& white LEDs (D1 & D6).
Transistors, such as the NPN transistor (Q2),
can amplify electric currents. In this circuit,
the adjustable resistor controls a small
current going to the transistor through the
red LED. The transistor uses this small
current to control a larger current through the
white LED. At some RV settings, the control
current is too small to light the red LED, but
the transistor-amplified is large enough to
light the white LED.
The PNP transistor (Q1) is just like
the NPN transistor (Q2), except that
the currents flow in opposite
directions.