I was recently given a maths question as part of test.

The question.

You have a round coil core 10mm thick  and 50 mm long. You wrap a copper
wire exactly 5 times around. How long is the wire? (don t consider the
thickness of the wire)

__________________

The "trick" is in the interpretation of the question, which is not as clear
as it should be.

The "clue" to their mindset is that they gave you the cylinder width which
is irrelevant unless you need it for some reason. While people may indeed
give you redundant data, Occam opines that they here intend you to use it.

So - when they say "exactly times around", which may or may not have been
their wording, they mean that the wire starts at a point on the say left of
the cylinder and ends at a point on the right of the cylinder 50mm along
the cylinder from the start. ie it extends evenly from side to side of the
spool even though it (almost certainly) does not tightly pack on the spool.

They do not need the multiple triangle gymnastics, I wot. Lets see.
Distance rotationally =3D L =3D 2 x Pi x r x 5 =3D 50 Pi =3D 157 as you hav=
e
calculated
Distance sideways =3D W =3D 50mm
Length is sqrt (l^2 + W^2) =3D 164.7 =3D 165mm

ie same result as theirs with only one triangle visualised.

Wire is not close packed as long as wire diameter is under 10mm (in which
case the wire thickness would make a major difference in real life.


      Russell
--=20
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