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Resistor value

Chassis

Apr 21, 2015
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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.
 

ramussons

Jun 10, 2014
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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.

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

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Sep 5, 2009
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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
 

Chassis

Apr 21, 2015
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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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davenn

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Calculate the following:

(a) The value of the current flow through R1, if I total = 4 A.




(b) The total overall resistance of R1 and R2 in parallel

do you know how to work out parallel resistors ?

(c) Determine the value of R3

you are already told it is 120 Ohms


(d) The total resistance of the circuit

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


Dave
 
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Chassis

Apr 21, 2015
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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?
 

Kiwi

Jan 28, 2013
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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?
 

davenn

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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???


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

Chassis

Apr 21, 2015
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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.
 

Chassis

Apr 21, 2015
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Or can someone please send me a link of series-parallel resistor circuit samples including questions and answers.thanks in advance guys.
 

Arouse1973

Adam
Dec 18, 2013
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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.

Do you have a copy of the exam paper with that question?
Adam
 

Chassis

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

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  • (BASTEC3)%20(E258)%20Basic%20Electronics%201%20(June2014)%20v5.pdf
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BobK

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

Bob
 

Chassis

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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.
 

Arouse1973

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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.
Adam
 

davenn

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I think they want you to show the workings of how you would determine the value of the resistor including the other two.

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
 

Chassis

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Anyone have links with series-parallel Resistor circuit Exercises?
 

davenn

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Anyone have links with series-parallel Resistor circuit Exercises?

please show a little effort ....
Im sure you are capable of typing that into google ;)

Dave
 
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