Electrical Theory - Resistor vs. mA

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kelly1

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I have been trying to answer a question in Electrical Theory and cannot figure out the answer. The question is: A 242Q resistor is in parallel with a 180Q resistor, and a 420Q resistor is in series with the combination. A current of 22mA flows through the 242Q resistor. The current through 180Q resistor is ______ mA.
Does anyone know the answer and can explain the formula for the answer?
 
Knowing the Ia & the resistence of one resistor tells you what the voltage drop across that resistor is. This voltage is the same on the parralel resistor. You have more than enough info now to solve for the Ia through the second resistor.
 
You can solve for the voltage across the 242Q resistor (I assume that Q is "Ohms") using Ohm's Law.

Because the 242Q and 180Q resistors are in parallel, the ends of their leads are connected together. The voltage that is on one resistor will be the same as the voltage on the other.

Since you have the voltage on the one, use that voltage, and Ohm's Law, again, to find the current in the 180Q resistor.

The 420Q is a red herring.
 
Yes, the Q does stand for Ohms. The question has a multiple choice answer. The choices are: 29.5, 40.2, 19.8 or 36.4. I still cannot figure the answer by your clues.
 
barbeer said:
22x242=5324v IxR=V
5324v/180=29.5 V/R=I

edit to add formulas.
Click to expand...
Kelly,

There's a bit of shorthand there, that is, the dropping of the decimal places.

22 mA = .022 A

.022 A x 242 Ohms = 5.324 V ( 5 kV is counter intuitive. . just shorthand).

I agree that the answer is 29.5 milliamps.

If you know the current and resistance of a resistor, you know the voltage across it.

Consider:
OhmsLawQuestion.jpg


If something else is "in parallel" with that resistor, the voltage on the resistor has to be the same voltage on the other something, as there is no voltage drop in the schematic conductor (real world conductor, yes, but not the schmatic conductor). So the voltage on the 242 Ohm resistor is the same voltage on the 180 Ohm resistor. Knowing the voltage and the resistance of the 180 Ohm resistor allows the application of Ohm's Law to solve for the current in the 180 Ohm resistor.
 
al hildenbrand said:
There's a bit of shorthand there, that is, the dropping of the decimal places.
Click to expand...

I am glad you pointed that out..........I battled within of showing it correct(with decimals) but decided to show him (or her) the simple way to get his (or her) answer.:smile:
 
Thanks to everyone for all your help. When I can mulitiply by 22 instead of 0.022 it sure made understanding this simpler.
Thanks again,
Kelly
 
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