Nodal Analysis- direction of currents flow

[user5]

The figure shows a transistor with a bias circuit. If I_c=50I_B and if V_BE=0.7V, find V_CE.

My question is:
The current through 700Ω resistor is H=[0.7+(51I_B(250))]/700,
then when KCL is applied at the left hand node, the current flowing through the 3kΩ resistor suppose to be (according to hint),H+ I_B. However isn't it suppose to be minus(H+I_B)? (since the currents drop through resistors equals minus I_B, it flows out of the node to the source)?

Thank you for any help you can provide.

 

[Jony130]

Well the correct answer is that the current flowing through the 3kΩ resistor is equal to H +Ib.
Why you think that H - Ib is correct answer ?

 

[user5]

-For the nodal analysis (at the left-hand node), does the part towards the current I_B flows regarded as resistor? (By that I mean shouldn't the transistor part be regarded as a current source?)

- Does the direction of flow through 3kΩ and 700Ω resistors is downwards due to the polarity of the voltage source 9V?

Thanks in advance.

 

[sophiecentaur]

With the battery 'that way up', current will be flowing from top (+) to bottom (-) of the circuit. Thus, the current through the 3k will split through the lower resistor and the base.
The base of a transistor does not appear as a constant current - just a high resistance, when an emitter (voltage feedback) resistor is in place; it is the collector which approximates to a constant current source.
I think I would re-write your equation

H=[0.7+(51IB(250))]/700

as H=[0.7+(IE(250))]/700, initially, and develop it from there (if you haven't already done so).

 

[Jony130]

The base current in NPN transistor always flow into the base. Flow in direction show by the arrow in your diagram.

- Does the direction of flow through 3kΩ and 700Ω resistors is downwards due to the polarity of the voltage source 9V?

Yes, simply current flow from "+" to "-". And we have "+" at top and "-" at the bottom.
So when looking at schematics, most people get comfortable with the general notion that things flow top to bottom and left to right.

 

[user5]

sophiecentaur : Thank you very much!

Jony130: Thank you very much!