resistors in parallel

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NWDS

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Afternoon fellas 7 ladies, Iam struggling with the above, I have the elec calcs ( vol 1 7th ed ) and I cannt seem to get the figures for the answers I get very near but not an exact match, any help would be appreciated.

regards Iain

 

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Give an example of what you are struggling with OP. :)

 

NWDS

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Afternoon fellas 7 ladies, Iam struggling with the above, I have the elec calcs ( vol 1 7th ed ) and I cannt seem to get the figures for the answers I get very near but not an exact match, any help would be appreciated.regards Iain
can you work out

1 at 4 ohms

1 at 6 ohms

1 at 9 ohms

connected in parallel what is the equivelant resistance ?? make the answers correct to 3 significant figs.

 

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RT = 1/4Ω + 1/6Ω + 1/9Ω = 1/RTΩ

RT = 0.25Ω + 0.166Ω + 0.111Ω = 1/1.021Ω = 0.979Ω

Is that what you are looking for?

 

NWDS

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no the book says 1.89 ohms

I got

1 at 0.25

1 at 0.16

1 at 0.11

added up = 0.52

1 divided by 0.52 = 1.92 ohms

 

NWDS

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Some of the answers in the book I get and some I donnt, I use the same formula all the time this is what is throwing me !!!!!!!!!!!.

thanks Iain

 

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The clue is in the "Significant figs"

So it will be:

0.25Ω + 0.17Ω + 0.11Ω = 0.53Ω = 1/0.53 = 1.886 1.88679245283019

Rounded is 1.89Ω

 

NWDS

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0.25+0.166+0.111 = 0.527

1 divided by 0.527 is 1.89

I think that is how it should be ( I was only using 0.16 & 0.11 )

regards Iain

 

NWDS

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Thanks fellas, that is the benefit of this site.

regards Iain

 
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can you work out 1 at 4 ohms

1 at 6 ohms

1 at 9 ohms

connected in parallel what is the equivelant resistance ?? make the answers correct to 3 significant figs.
The other way you can check Parallel resistors is use the "Product" over "Sum" method.

e.g.

two resistors R1 & R2 in parallel.

res = (R1 x R2)/(R1 + R2).

with 3 resistors you can calc two of them first then Calc third afterwards..

i.e.

4 & 6 in parallel is (4x6)/(4+6) = 24/10 = 2.4

now do

2.4 & 9 in parallel is (2.4x9)/(2.4+9) = 21.6/11.4 = 1.89473 etc.. =1.89

which proves you have your calc correct using the other 1/R1 + 1/R2 + 1/R3 = 1/Rx method.

 
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