Data Sheet
-82-
150. Transistor Gain b
Build the circuit shown on the left and turn on the switch (62). Place the magnet
(7) near the reed switch (83) and you will see the star LED (70) light. Move the
magnet (7) away from the reed switch (83) and the star LED (70) will stay bright
for a little while and then turn dim. Transistors like the NPN transistor (50) can
be used as ampliers where a small current into the Base can be “amplied” to
produce a large current out of the Emitter. The gain of the NPN transistor (50)
is dened as the ratio of the Collector current to the Base current and called b
(pronounced Beta). If you had an ammeter and measured the current going into
the Base it would be around 3.7 mA, while the current coming out of the Emitter
would be about 42 mA. This yields a b = 42/3.7 = 11.4.
151. Transistor Gain with 5.1kW Resistor
Replace the 1kW resistor (42) in project #150 with the 5.1kW resistor (43)
and turn on the switch (62). Place the magnet (7) near the switch (83) and
you will see the star LED (70) light. Move the magnet (7) away from the reed
switch (83) and the star LED (70) will stay bright for a while and then turn
dim. If you had an ammeter and measured the current going into the Base it
would be around 0.75 mA, while the current coming out of the Emitter would
be about 41 mA. This yields a b = 41/0.75 = 55.
152. Transistor Gain with 10kW Resistor
Replace the 1kW resistor (42) in project #150 with the 10kW resistor (44)
and then turn on the switch (62). Place the magnet (7) near the reed switch
(83) and you will see the star LED (70) light. Move the magnet (7) away
from the reed switch (83) and the star LED (70) will stay bright for a several
seconds and then turn dim. If you had an ammeter and measured the current
going into the Base it would be around 0.37 mA, while the current coming
out of the Emitter would be about 41 mA. This yields a b = 41/0.37 = 111.
153. Transistor Gain with 100kW Resistor
Replace the 1kW resistor (42) in project #150 with the 100kW resistor (45)
and then turn on the switch (62). Place the magnet (7) near the reed switch
(83) and you will see the star LED (70) light. Move the magnet (7) away from
the reed switch (83) and the star LED (70) will stay bright for a long time
and then turn dim. If you had an ammeter and measured the current going
into the Base it would be around 0.038 mA, while the current coming out of
the Emitter would be about 10.6 mA. This yields a b = 10.6/0.038 = 279.
As seen in the last three projects, the b of the transistor is different for each
project. This is because the b of a transistor is not a constant but a function
of the current through the transistor.
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