# Vb in transistor questions

1. Apr 25, 2012

### Femme_physics

In a transistor...

If a question asks me to find Vb, do they mean the voltage from the base to the ground, or the voltage on the base resistor?

The question I have does not specify, it just says "find the base voltage, Vb"

So I have 2 Vb's and I'm not sure which one they're asking for...

http://img39.imageshack.us/img39/3839/vbbok.jpg [Broken]

Last edited by a moderator: May 5, 2017
2. Apr 25, 2012

### Staff: Mentor

Single letter subscripts for voltages usually refer to the voltage of that terminal with respect to ground. Thus Vb (or Vb for subscript impaired documents) would be the potential at the base with respect to ground.

Double letters refer to potentials between terminals. Thus Vbe would be the potential at the base with respect to the emitter.

3. Apr 25, 2012

### Staff: Mentor

Hi FP! There is a strict convention involving upper and lower case, both for the V and the subscripts. When you are talking about DC (or average) levels, you use capital "V" and capital subscripts, so base voltage would be VB.

If you were talking about just the AC component (i.e., the audio signal your circuit is amplifying), then you use lower-case "v" and lower-case subscripts, e.g., vb.

There is more, but if you follow this much you'll be off to a good start.

Yes, VB is from base to ground.

4. Apr 27, 2012

### Femme_physics

Thanks for clearing it up :)

5. Apr 27, 2012

### Staff: Mentor

And if conventions were being correctly followed, there would be only one VB in your schematic, anyway, so no room for confusion. The other one would be VRB.

6. Apr 27, 2012

### Femme_physics

Ah...dooly noted :)