2391 question

[scampi220880]

two identical conductors are to be connected in parellel. each conductor measures 60m in length and has a resistance of 1.15 Mohm/m what is the combined resistance of the condutors show all calculations


I have 2 seperate past papers and answers with this question on and have 2 different answers does any 1 know the correct formula
thanks for any help

 

[mattmoo1974]

60x1.15/1000x2 at a guess.
But you dont want a guess, So wait til some 1 really clever posts
Being in parallel as well.

 

[High Tower]

60 x 1.15/ 1000 =.069

So each conductor will have a rounded up resistance of 0.07, and as they are in parallel then it is the fractional method of -

1/RT= 1/R1+1/R2 etc

So 1/0.07 = 14.2 +1/0.07 (14.2)

so RT = 28.57

So 1/RT = 0.035

 

[Sparky Ninja]

I just worked it out to approximately 0.035 ohms, exactly as High Tower has.
I would normally be looking for a factor to apply, but if it's not in the question then it can't be used.

 

[High Tower]

The is a 1/ butrton on most scientific calculators that make it a lot quicker,

Just remember as a rule of thumb, your answer is ALWAYS lower than your lowest given resistance

 

[Jurasic Spark]

Its a golden rule of resistors in parallel that 2 of the same value is the same as 1 of half that value

 

[Guest123]

Using resistors in parallell sum 1/RT = 1/R1 + 1/R2 etc etc I get 0.035ohms


EDIT: note to self......must type faster!!

 

[Sparky Ninja]

I'm intrigued as to what the two different answers are that the OP has in regard to this question??

 

[scampi220880]

these are the answers i was given
(1.15x60)+(1.15x60) 1.15+1.15x60
divided by diveded by
4 = 34.5 m ohm and 1000 = 0.138 ohms

so know im really confused

 

[Guest123]

I'm intrigued as to what the two different answers are that the OP has in regard to this question??

Wouldn't surprise me if 2.30 was one of the answers......

 

[Sparky Ninja]

these are the answers i was given
(1.15x60)+(1.15x60) 1.15+1.15x60
divided by diveded by
4 = 34.5 m ohm and 1000 = 0.138 ohms

so know im really confused

Where did you get these from??

 

[mattmoo1974]

Im thinking hes thinking its a ring?
Hes in radialville!

 

[High Tower]

Ring circuit would be =

1.15x60/1000 = 0.07

0.07x2 = 0.14

Interconected and tested on the ring =

0.14/4 = 0.035 at each point

 

[scampi220880]

the answers never came out as planned
(1.15x60)+(1.15x60)/4= 34.5m ohm
and
(1.15+1.15)x60/1000 = 0.138 ohms

 

[High Tower]

Ok your first one is a calculation for a ring as i have demonstarted and the second you have not calculated for resistence in parallel 0.138 would be correct if it was a series calculation, however we never connect circuts in series.