b. With the meter connected across the emitter-collector circuit with an open
condition, the meter measures 1K since the current flows out the negative lead
through the 1K resistor to the positive meter lead. For this reason, whenever you
check a transistor, two of the three leads must be disconnected from the circuit.
c. A transistor, like a diode, has a low-resistance junction when it is
forward-biased and a high resistance when it is reverse-biased.
When the meter
leads are connected red to base and black to emitter, the lowest value of
resistance is measured. This indicates a forward-biased condition.
d. When the E-B junction is forward-biased, a negative potential is applied
to the base.
You remember from your study of diode testing, this indicates that
the base is constructed of N-type material and that the emitter is constructed of
P-type material. Once you know the type of material that the base and the emitter,
or collector, are made of, you can determine the type of transistor. Since we know
the emitter is P-type material and the base is N-type, this must be a PNP-type
transistor.
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