# Open Resistors

#### MeltedOzark

Joined Nov 8, 2011
3
Hello electrical enthusiasts, my friend and I require assistance for our electronics class.

We have to find the voltage drops in a series circuit with 5 resistors, the 3rd of which is open. Now, as far as I know, this resistor gives infinite resistance, so we don't understand how we calculate current for the circuit (the only method we know being V/R).

Now, our knowledge on circuits is extremely limited, so it would be greatly appreciated if someone explains this in simple terms. Thanks in advance for any help Joined Dec 26, 2010
2,148
You already have a valid formula for the current in the circuit: I = V/R.

As you say, if a resistor is open, it has infinite resistance. What then is the circuit current?

#### crutschow

Joined Mar 14, 2008
27,718
Hint -- The question is: where does the voltage drop occur and how much is it?

#### MeltedOzark

Joined Nov 8, 2011
3
The question asks for the voltage drops at all the resistors, but if the current is zero, there aren't any voltage drops?(meaning its a trick question). Or just a big drop at the battery? As the total voltage for the circuit is 24V.

#### praondevou

Joined Jul 9, 2011
2,942
The question asks for the voltage drops at all the resistors, but if the current is zero, there aren't any voltage drops?(meaning its a trick question). Or just a big drop at the battery? As the total voltage for the circuit is 24V.

You are almost there.

If the current is zero then there are no voltage drops on the resistors that are not broken. V=IxR

Now I wonder how we could solve the voltage drop on the broken resistor with the formula V=IxR. Is that zero multiplied with infinite?

If the total voltage is 24V and there is no voltage drop on the intact resistors then the total voltage appears at: ?

#### crutschow

Joined Mar 14, 2008
27,718
Or: If you put a voltmeter across each resistor, one at a time, what would you measure for each resistor?

#### MeltedOzark

Joined Nov 8, 2011
3
So the voltage drop at R1,2,4,5 is 0, while R3 is 24?

If that's correct, I totally understand it, and I thank you gentlemen #### praondevou

Joined Jul 9, 2011
2,942
So the voltage drop at R1,2,4,5 is 0, while R3 is 24?

If that's correct, I totally understand it, and I thank you gentlemen That's it.