Question?

[Wardy35]

Question:- A conductor has a cross-sectional area of 20mm2, a length of 48m and made of material with a resistivity of 0.02 micro ohms per meter, what is its resistance?

Once i get loads of answers i will tell you why i asked it.

Regards
Mick Ward

 

[pmac10]

resistance=constant of proportionality(0.02)*length(48) divided by cross sectional area(20)
answer=0.048

 

[GrannySmiff]

Resistance = pxl/a = 0.02x10minus6 x 48 / 20x10minus3 = 4.8ohms

 

[JulianC]

The answer is d) 0.048 ohms

R = pL/A

It is important to get your units standardised into ohms and metres and not a mixture of mm, micro-ohms etc, otherwise your answer will be wrong.

So we get:

p = (0.02 x 10 to the power -6) to convert it to ohms/metre = 0.00000002
L = 48m
A = 0.00002 metres squared

Therefore

R = 0.00000002 x 48 / 0.00002

= 0.048 ohms

 

[pmac10]

julian, thanks for confirming my answer, but inputting the original figures give the same answer, though you are correct about standardised units

 

[JulianC]

but inputting the original figures give the same answer

Just happens to be a happy coincidence in this case. If p was given as 0.02 milliohms for example, the answer you get by just plugging in the original figures would be wrong.

As it stands, the factor to convert micro ohms to ohms just so happens to be the same as the one to convert mm squared to metres squared so they cancel each other out.

Therefore, you have as much chance of getting the correct answer if you have not got a clue how to do it. (Not that I am inferring you do not have a clue of course!)

 

[pmac10]

Just happens to be a happy coincidence in this case. If p was given as 0.02 milliohms for example, the answer you get by just plugging in the original figures would be wrong.

As it stands, the factor to convert micro ohms to ohms just so happens to be the same as the one to convert mm squared to metres squared so they cancel each other out.

Therefore, you have as much chance of getting the correct answer if you have not got a clue how to do it. (Not that I am inferring you do not have a clue of course!)

your preaching to the converted mate, i, like yourself, know my stuff, was merely making an observation and didnt want to confuse any further a lad whose op has gone to two pages

 

[mayfair]

You could always copy of the bloke sitting next to ya, and hope he's got it right

 

[Wardy35]

Cheers gents i may not have had to ask this question if the so called workbook i am working from told me to standardise the units, thank god for this forum and you clever and understanding people.

Thanks

Mick