Transistor junction check (silicon NPN): With a digital ohmmeter's positive probe placed on the base terminal, what type of reading should you expect when measuring from base to the other two terminals (base–emitter and base–collector)? Assume a standard diode-test/ohms function.

Introduction:
A quick health check for BJTs uses an ohmmeter or diode tester to evaluate the two internal PN junctions. Understanding expected readings helps technicians identify open or shorted junctions without powering the circuit. This question targets the expected readings for a silicon NPN transistor when the positive meter lead is on the base.

Given Data / Assumptions:

• Device under test: NPN BJT (silicon).
• Meter positive probe on base; negative probe touching emitter or collector.
• Meter in ohms/diode test mode with small forward test current.
• Transistor not connected to a powered circuit during measurement.

Concept / Approach:
An NPN contains two PN junctions: base–emitter (P–N) and base–collector (P–N). With the positive probe on the P-type base and negative probe on N-type emitter or collector, each junction is forward-biased. A forward-biased diode shows a low resistance (or about 0.6–0.7 V on diode scale). Reversing the leads should show high resistance, indicating a good junction.

Step-by-Step Solution:
Place positive probe on base and negative on emitter: forward-biased P–N → low resistance/diode drop.Move negative probe to collector: again forward-biased P–N → low resistance/diode drop.Reverse polarity (negative on base, positive on emitter/collector): reverse-biased → high resistance/open on typical ohms range.Consistent low forward readings and high reverse readings indicate healthy junctions.

Verification / Alternative check:
On a diode tester, a good silicon NPN shows ~0.6–0.7 V from base to emitter and base to collector with the positive lead on base, confirming low forward impedance in that direction.

Why Other Options Are Wrong:
Open / infinite / high resistance: these correspond to reverse bias or a damaged/open junction; not expected when forward-biasing with positive on base.

Common Pitfalls:
Touching probes improperly or testing in-circuit (sneak paths can mislead). Always isolate the transistor or at least lift leads for reliable junction checks.

Final Answer:
low resistance