Question about circuits (currents going into nodes)

[doctordiddy]

So according to kirchhoffs junction rule, all currents entering a node must be equal to currents exiting a node. In this example

http://imgur.com/4Zqb21A

If we take a node as the point between the 4 ohm resistor, 5 ohm reisistor, and the 20V battery, how would you be able to determine an equation or currents?

For example, if I1 is the current through the 2ohm battery, I2 the current through the 4ohm, and I3 the current through the 5 ohm, how can you write this relationship?

I1=I2+I3?
I2=I3+I1?

How can you determine which currents are entering and exiting a node?

Thanks for any help

 

[SammyS]

So according to kirchhoffs junction rule, all currents entering a node must be equal to currents exiting a node. In this example

http://imgur.com/4Zqb21A

If we take a node as the point between the 4 ohm resistor, 5 ohm reisistor, and the 20V battery, how would you be able to determine an equation or currents?

For example, if I1 is the current through the 2ohm battery, I2 the current through the 4ohm, and I3 the current through the 5 ohm, how can you write this relationship?

I1=I2+I3?
I2=I3+I1?

How can you determine which currents are entering and exiting a node?

Thanks for any help

You must pick a definite direction for each of those currents.

 

[doctordiddy]

how would you tell which two are going in the same direction and which one is going in the opposite direction?

 

[SammyS]

how would you tell which two are going in the same direction and which one is going in the opposite direction?

It's totally up to you to pick the direction, if it's not given to you.

Then you work out the problem, finding all the currents. Some may turn out to be negative, which simply means the current actually flows opposite to the direction you chose.