Series-Parallel circuit

[Deathshead]

Can you guys tell me if these nominal values are correct for the circuit:

The Voltage is 12V
R1 and R2 are in parallel
and R3 is in series with R1R2


VR1=4v
VR2=4v
VR3=8v
IR1=4mA
IR2=4mA
IR3=8mA
IT=16mA

 

[Russlk]

Yes.

 

[Deathshead]

oops, i forgot to mention that they were all 1k resistors, is that still correct?

 

[Deathshead]

im not to sure about the IT because according to ohms law isnt it (IT=V/R) 12/1500 which is equal to 8mA. So im confused as to wether IT=8mA or if i add all the I values and leave it as 16mA

 

[k7elp60]

series parallel circuit

I figure the total current is 8 Ma.

 

[Geordie340]

Deathshead,

when dealing with currents in a circuit you have to use Thevenins theorem when looking at the devices, and not simple add the currents of each of the devices. (the Algebraic sum of the currents at any node is equal to 0). So if you know your total equivalent resistance for the circuit and the input you can calculate the total current using ohms law.

This total current is then shared to go through parallel devices in the circuit, while series devices will get the whole lot.

eg in your circuit since all are 1K and youve calculated total current as 8mA, the two parallel resistors will each get an equal share (4mA) if the third resistance is then in series with these parallel two, the node between the 2 will sum as +4+4-8=0, ie 2x4mA into the node 8mA out and through the third resistor.

Sorry if this isn't too clear, I think I gave too much information (Simply put, your IT is calculated using ohms law with your equivalent RT, if you want to understand why this is the case then look at Thevenins), too late for theory, if you need a better explaination let me know and I'll sort one out for you.

 

[Painandsuffering]

IT

Yes the Current total or IT will be 8ma since your two parallel resistors are taking 4ma each you can just add them together. I think you got the 16ma from accidently adding in the current across R3 which is in series which makes it a voltage divider not a current divider so current through it will be 8ma or the total current.