Very simple question needs answer !

[ElectroNewby]

Hello. Today, I started school. We will have a test in about a month, tho when haven't seen anything yet. I wanted to check out a bit of what we will have to learn.

I found this question:
Evaluate the current in Amperes in the resistance R1 (4 ohms) when Vs = 72 Volts and R2 = 4 Ohms

I ended up with 36A because I said Rt=2ohms. (i think it's parralel and 2 resistor of same value, you divide by 2, right ?)

It looks like this. Please if you can shed me light. Tell me how am I wrong ?

|----r1----|------
---|----r2----|

 

[colin55]

If they are in parallel, 18 amps will flow in R1 and 18 amps will flow in R2.

 

[gelbschnee]

for resistors in a parallel circuit, the voltage will be equal on all resistors, and current is divided up among each resistor depending on its value (lower resistance allows more current to pass). In your case, both resistors are of equal value, so they current is also equal.

 

[ElectroNewby]

Thanks men ! If I'd need to find the total of I in the source Vs=18V when the resistors are NOT equal (R1 = 5 ohms and R2 = 4 ohms) is that much of a big deal ?

My noobish questions... Today in college they just talked about the course and notation... not much about what we are going to learn. When haven't seen anything yet but I want to understand bits and bites before we start... I want good marks but I finished highschool 0,01 x 10^3 yrs ago... ;P
I do know that V=IR and can turn it around easily (I =V/R, R=V/I). I know a bit about the AGW, the mils. the Joule/Coulomb/Amp/Electrons and stuff... but not quite the formulas and parralel/mixed or Kirckoch's law yet. I can't wait to learn how to play it tho, wish me luck/fun (sorry for that slice of life).

 

[gelbschnee]

this will help: total resistance of a parallel circuit =

1 / R1 + 1 / R2 + 1 / R3 +...

if you have any more questions please ask this is a great thread for people to learn...

 

[timmytandian]

kirchof's current law: current at any node algebraically sum to zero. In other word the sum of current that enter any node is equal to current that leave the node.
kirchof's voltage law: voltage at any loop algebraically sum to zero. In other word the sum of voltage rises is equal to voltage drops on any loop.

Kirchof's law are powerfull for many problems (but not all).

 

[misterT]

this will help: total resistance of a parallel circuit =

1 / R1 + 1 / R2 + 1 / R3 +...

if you have any more questions please ask this is a great thread for people to learn...

That equation is wrong.

 

[parthshah08]

Your ans would be certainly 18A through R1 and r2 both

 

[parthshah08]

How come that equation is wrong for parallel resistors?

 

[misterT]

this will help: total resistance of a parallel circuit =

1 / R1 + 1 / R2 + 1 / R3 +...

if you have any more questions please ask this is a great thread for people to learn...

That equation is wrong.

How come that equation is wrong for parallel resistors?

The reciprocal of total resistance of a parallel circuit = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn

**broken link removed**