# Resistor value

Discussion in 'General Electronics Discussion' started by Chassis, Jun 4, 2015.

1. ### Chassis

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Apr 21, 2015
Good day.I have a question,I'm sorry if it may sound stupid. To what does it refer if you get a question as "Determine the value of R3" if R3 is 120Ohms.does it refer to the color code? Brown,Red,Brown? The question doesn't say anything about color codes.

2. ### Y2KEDDIE

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Sep 23, 2012
Possibly it's wattage rating.

3. ### ramussons

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Jun 10, 2014
How did this value of 120 Ohms come from? Was there a calculation?
Can you ask the question in a different style?

"value of R3" can only be "Ohms",

davenn likes this.
4. ### davennModerator

13,929
1,980
Sep 5, 2009
show us the full question and any circuit pic associated with it

the Q is obviously referring to a circuit that you haven't told us about

5. ### Chassis

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Apr 21, 2015
Sorry for the bad quality.all the questions for the circuit is below.I understand everything except the one above.

For the given circuit we have the following:
R1 = 200 ohm, R2 = 50 ohm and R3 = 120 ohm
The volts drop V3 across R3 is measured as 160V
Calculate the following:

(a) The value of the current flow through R1, if It = 4 A.
(b) The total overall resistance of R1 and R2 in parallel
(c) Determine the value of R3
(d) The total resistance of the circuit

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6. ### davennModerator

13,929
1,980
Sep 5, 2009

do you know how to work out parallel resistors ?

you are already told it is 120 Ohms

work out the parallel value and add it to the 120 Ohms

Dave

Last edited: Jun 5, 2015
7. ### Chassis

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Apr 21, 2015
The question they are asking sounds very senseless if they already giving it to me (120 Ohm) I am sorry I waisted your time. So the resistor value always refers to the resistor Unit?

8. ### Kiwi

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Jan 28, 2013
I am a little confused.

They give R3 value as 120Ω and voltage drop as 160V.
Using Ohms Law: I = V/R = 160/120 = 1.333Amps.
In (a) they give It as 4A, so V = I x R = 4 x 120 = 480V
What happened to the given voltage of 160V???

(b) Parallel resistance of R1 and R2 network is easy enough to calculate using 1/Rp = 1/R1 + 1/R2

(c) They have already given you resistance of R3 as 120Ω. Maybe they want wattage of R3 using P = V x I. What voltage do you use?

(d) Total resistance = Rp + R3

What am I missing, or is the question all messed up?

9. ### Chassis

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Apr 21, 2015
Refers to the resistor Ohms?

10. ### davennModerator

13,929
1,980
Sep 5, 2009

yes I saw that too ... it just doesn't make sense ... there seems to be too many errors in this question

11. ### Chassis

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Apr 21, 2015
This question was asked in last years exam papers. can someone work this out or draw a circuit with more or less the same questions and answers in order for me to apprehend it.

12. ### Chassis

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Apr 21, 2015

5,164
1,087
Dec 18, 2013
Do you have a copy of the exam paper with that question?

14. ### Chassis

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Apr 21, 2015
I hope the attach will open,its pdf format.check out page 5.

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15. ### BobK

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Jan 5, 2010
Yes, the question is self contradictory. If It is 4A, and V is 160, then R3 has to be 40Ω.

Bob

16. ### Chassis

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Apr 21, 2015
Got you there Bob! So the reason why they have mentioned R3 as 120ohm refers only to question (d) ? that's if you managed to open my attachment.

5,164
1,087
Dec 18, 2013
I think they want you to show the workings of how you would determine the value of the resistor including the other two. You would also have to indicate the supply voltage also.

18. ### davennModerator

13,929
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Sep 5, 2009
that's pointless, as said earlier, the value is given, there isn't anything to calculate

Q parts a, b and d are valid.
c doesn't make sense when it's already given and as again already been stated earlier
I total cannot be 4A if the V drop across 120 Ohms is 160V

the whole Q has a lot of problems

19. ### Chassis

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Apr 21, 2015
Anyone have links with series-parallel Resistor circuit Exercises?

20. ### davennModerator

13,929
1,980
Sep 5, 2009
please show a little effort ....
Im sure you are capable of typing that into google

Dave