# Another Transistor Circuit Problem

#### DYLH

Joined Aug 13, 2013
28
For this practice problem, I don't see how the answers make sense.

From Ohm's law
V = IR
Vo = Io * 10,000
= 600 (10^-6) * 10,000 = 6

But Vo according to the Answer is 12.

How are they getting 12V and 600uA?

TIA_

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#### Jony130

Joined Feb 17, 2009
5,351
Have you try to write KCL for Vo node?

#### #12

Joined Nov 30, 2010
18,223
The example must be wrong. 12V/10K can't possibly result in a current that starts with "6".

#### Jony130

Joined Feb 17, 2009
5,351
My answer is Vo = 9V and Io = 900μA

#### DYLH

Joined Aug 13, 2013
28
Thanks, Jony130.. that's exactly what I got.

#### WBahn

Joined Mar 31, 2012
26,422
Is this also from Fundamentals of Electric Circuits by Alexander and Sadiku 5th edition?

There is a disturbing pattern developing here.

Are you finding very many of their problems have incorrect solutions? Or is it just that we are only seeing the very few that have issues?

Aside from that, it's a bit troubling that they are having you spend a lot of time analyzing circuits in which the answer is completely dependent on the transistor beta. Now, if they are just introducing the concept of transistors, that is not too unreasonable. But hopefully they have already pointed out that transistor beta is a very unreliable parameter and that if varies all over the place with temperature, current, voltage, from transistor to transistor, and with the phase of the moon. Then, hopefully, they will soon move on to circuit topologies in which that variation only has minimal impact on the circuit's behavior.