Homework Help: Thevenin equivalent resistance problem

Hello glover261. Welcome to PF !

So far, so good.

What have you been taught regarding how to find the Thevenin equivalent resistance ?

 

That's not quite right. You don't simply add all the resistances. You find the equivalent resistance across the terminals.

 

Is "adding up the total resistance of all the resistors" really what happens in a circuit? Do parallel resistors add?

EDIT: I see sammy beat me to it.

 

You must be missing something.

Draw what you have when the voltage source is shorted.

 

Probably be a good idea to go back to basics and study what parallel and series really look like. This is a very common difficulty in beginning study of circuits so it's best to get really solid with it in the beginning.

EDIT: dammit, sammy, you're too fast for me

 

Probably be a good idea to go back to basics and study what parallel and series really look like. This is a very common difficulty in beginning study of circuits so it's best to get really solid with it in the beginning.

 

See the terminals?

(phinds beat me this time !)

 

See the terminals?

 

Find the equivalent resistance across the terminals.

Look at the nodes again.

 

There is an alternate way to find the Thevenin resistance.

Take the original circuit, and find the current which flows through a wire which is connected to the two terminals. (This is the short circuit current.)

This is the same current which will flow through the Thevenin equivalent circuit if its terminals are shorted.

In other words, this current times the Thenenin resistance is equal to the Thevenin voltage.