Electronics - Bipolar Junction Transistors (BJT) - Discussion

The correct answer is: "low resistance".

Explanation:

An NPN transistor has two PN junctions:

1. Base–Emitter (BE) — behaves like a diode (P to N)
2. Base–Collector (BC) — also behaves like a diode (P to N)

When you place the positive (red) probe on the base of an NPN transistor and touch the negative (black) probe to either the emitter or collector:

* You are forward-biasing the BE or BC junction.
* This gives a low resistance reading (just like a forward-biased diode).

So, the reading between base and emitter or base and collector will show low resistance.

Note:

* Reversing the probes would show high or infinite resistance because the junctions would be reverse-biased.

When NPN base is conected to P-terminal or P-probe, the transister will operate under forward bias. In forward bias the deplition layer decreases. Then more number of electrons & holes will move from one region to the other region. Hence the resistance becomes low.

No @yadhunanda it is rite ! low resistance between both emitter and base as well as base and collector since emitter and collector both will have the negative terminals of the probe ! and hence it will always make a forward bias circuit.

When the positive probe of ohmmeter is placed on the p-type base in the transistor, it makes the condition of forward bias and we know that in forward bias resistance is low. That is the reason for the low resistance.

But the question is that they ask that if p terminal of supply is connected with p terminal of npn transistor what should be the reading of ohm meter with other two terminals not only for emitter terminal.

In npn transistor, base terminal is of p-type. So, when the probe positive terminal is kept on ptype of transitor, now it is just like a transistor in forward bias, which offers a low resistance.

In NPN transistor, base terminal is of p-type. So, when the probe positive terminal is kept on ptype of transitor, now it is just like a transistor in forward bias, which offers a low resistance.

Base connected the +ve terminal it's forward biasing condition. Collector base depletion region is high similarly emitter-base depletion region is low compared to CE. So, it's low resistance.

Here question is not correct if positive terminal is there on the base of npn transistor low resistance between base and emitter terminals, high resistance between collector and base.

Since base is conneted to +ve probe it has a higher potential than other terminals so it makes the transistor in forward bias mode for both terminals. Hence low resistance.