Multiple Choice Exam at work - can you answer this...?

[mail2neil]

I have had to fill in a 'test' at work about elctricity.
The shocker for me was this question;

Which materials are good conductors of electricity? (select all the apply)
A Copper
B Aluminium
C Trees
D Plastic
E Silver
F People


I would be grateful for your answers. I know the answer - I will post it in an hour or so..., but I got it tragically wrong, and I am still not convinced that my company is right...

Many Thanks

Neil

 

[BS3036]

Typical stupid question from someone trying to shock you, I suspect. It is meaningless unless you specify 'good'. In general metals conduct well.

I imagine that 'people' is the suspect answer. A typical person may have a resistance of around 50kOhms or more under normal conditions. Is that a good conductor?

[Living trees are lower in resistance than dried wood, but still in the MOhm region, if I recall correctly.]

 

[ceraunic_level]

Anything will conduct electricity if there is enough of it. Just think of air and lightning

The metals are in the following order

Silver
Copper
Aluminum

As for the others I would say

People
Trees
Plastic

Unless they are being tricksy and really mean to say people are bad conductors because it kills them..

 

[holmslaw]

..

 

[mail2neil]

Okay - so the 'correct' answer in the test was
Aluminium
Copper
Silver
Trees, and
People
are good conductors..

Where as being the clutz that I am... - I went for just the metals!

 

[BS3036]

You're not a klutz. The guy who worded the question is.

 

[holmslaw]

..

 

[TicklyT]

I can see an argument for calling trees, as opposed to wood, a conductor- there's a lot of water in a tree that's removed after it's cut and before it's sold as timber. Maybe not as much as should be, but that's another matter....

What's this word 'plastic' doing in the list? surely 'plastic' is a state, like 'solid', 'fluid' etc.

There is a large range of materials that exhibit plastic properties, including PVC, PTFE, polystyrene, polyethylene, mercury amalgam (as used by dentists) etc. etc.

Would anyone describe my last example as a poor conductor?

 

[DeadJoe]

Some plastics conduct electricity by design. They tend to be used in anti-static shoes and anti-static mats for electronics work.

 

[vsynth]

Of course trees are good conductors, I use them all the time when I am short of copper wire.

I would use people too but there are some ethical/moral issues with this

Given enough voltage just about anything will conduct electricity.

 

[NamelessRob]

A short, fat person has a lower resistance than a long, thin length of copper.

 

[leeco]

i am installing a 10kw shower what size tree should i use?

 

[CortinaV8]

4' silver birch

 

[BS3036]

From the very interesting 'Wood Handbook - Wood as an Engineering Material' (a free download from the United States Department of Agriculture, Forestry Service).

The electrical conductivity of wood varies slightly with applied voltage and approximately doubles for each temperature increase of 10°C (18°F). The electrical conductivity of wood (or its reciprocal, resistivity) varies greatly with moisture content, especially below the fiber saturation point.

As the moisture content of wood increases from near zero to fiber saturation, electrical conductivity increases (resistivity decreases) by 10 to the power of 10, to 10 to the power of 13 times. Resistivity is about 10 to the power of 14, to 10 to the power of 16 Ohm·m for ovendry wood and 10 to the power of 3 to 10 to the power of 4 Ohm·m for wood at fiber saturation.

A little lower in resistance than I'd remembered! It does depend on sticking probes well into the wet part though. Actually the same applies for people, though I don't try that often.

 

[RF Lighting]

sticking probes well into the wet part though. Actually the same applies for people