Dow does this work?

Tom Crispin said:

I'm not an expert at Physics - I have a B grade 'O' level. I teach
basic electrics to primary children, so my knowledge is somewhere
above (I hope) the level of complete imbecile.

I have a SON hub dynamo on my bike. From the generator to the front
light are two wires - no problems so far. The turning of a magnet
inside a coil (or the turning of a coil around a magent) gets
electrons moving - exactly how it happens is beyond my understanding,
but that's not the point. When the electrons encounter the resistance
of the front bulb they glow, making light - a simplistic explaination,
I know. The electrons, delpeted of some energy, then return to the
generator - a very basic explaination, perhaps, but understandable so
far.

My rear mudguard light had not been attached to the circuit. I
ordered a 2.4w front bulb, downgraded from a 3w bulb, and a 2m cable
to link the 0.6w rear light to the generator. I plugged the cable
into a socket on the B&M front light case. I ran the cable, with the
Rholoff gear cables to the rear mudguard, and through a hole to the
underside of the mudguard where it is taped to the underside (I may
superglue it later) and is run to the end of the mudguard where it
makes indirect contact with the bulb.

All would be fine and perfectly understandable if there was another
cable - but there is only one. So what happens to the electrons after
they pass through the rear bulb?

I always tell my primary school pupils that for a light to work a
circuit must be complete, and we perform endless investigations to see
if we can light a bulb with an incomplete circuit. To date, our
investigations have all been fruitless. My only thought is that
perhaps the bike's frame works as part of the circuit, but surely this
is not possible. The mudguard is plastic with metal supports,
attached to the rear rack, attached to the frame, with the front lamp
also attached to the frame. Surely the whole bike hasn't been
designed to allow it to be used as a circuit? But I can think of no
other explaination.

Can anyone enlighten me?

The mudguard is chromoplastic. This means it has a conductive foil
laminated into it (look really carefully at the cut edges). The lamp
earths itself via the mudguard, then the frame, to the front lamp which
has a metal body. Simple!

Ben Barker said:

Tom Crispin wrote:

Quoted message said:

Quoted message said:

My rear mudguard light had not been attached to the circuit. I
ordered a 2.4w front bulb, downgraded from a 3w bulb, and a 2m cable
to link the 0.6w rear light to the generator. I plugged the cable
into a socket on the B&M front light case. I ran the cable, with the
Rholoff gear cables to the rear mudguard, and through a hole to the
underside of the mudguard where it is taped to the underside (I may
superglue it later) and is run to the end of the mudguard where it
makes indirect contact with the bulb.

All would be fine and perfectly understandable if there was another
cable - but there is only one. So what happens to the electrons after
they pass through the rear bulb?
I always tell my primary school pupils that for a light to work a
circuit must be complete, and we perform endless investigations to see
if we can light a bulb with an incomplete circuit. To date, our
investigations have all been fruitless. My only thought is that
perhaps the bike's frame works as part of the circuit, but surely this
is not possible. The mudguard is plastic with metal supports,
attached to the rear rack, attached to the frame, with the front lamp
also attached to the frame. Surely the whole bike hasn't been
designed to allow it to be used as a circuit? But I can think of no
other explaination.

Can anyone enlighten me?

<groan>

Quoted message said:

Faraday's law states that: V=-Ndphi/dt

<snip rest as irrelevant>

Quoted message said:

Bit of a dodgy explanation, but reasonably right. As for the "1 wire"
circuit, it is very common to use the bike frame as part of the dynamo
circuit -

Hope this helps,

Well it would but you forgot the one wire bit is hanging on a plastic
mudguard, and it is that which requires explanation. The mudguard
isn't plastic but a cunning sandwich of metal and plastic. The fixings
for the light and the stays go through the metal and thus in
conjunction with the bike frame complete the circuit from bulb to
dyno.
--
Phil Cook looking north over the park to the "Westminster Gasworks"

Tom Crispin said:

I'm not an expert at Physics - I have a B grade 'O' level. I teach
basic electrics to primary children, so my knowledge is somewhere
above (I hope) the level of complete imbecile.

I have a SON hub dynamo on my bike. From the generator to the front
light are two wires - no problems so far. The turning of a magnet
inside a coil (or the turning of a coil around a magent) gets
electrons moving - exactly how it happens is beyond my understanding,
but that's not the point. When the electrons encounter the resistance
of the front bulb they glow, making light - a simplistic explaination,
I know. The electrons, delpeted of some energy, then return to the
generator - a very basic explaination, perhaps, but understandable so
far.

My rear mudguard light had not been attached to the circuit. I
ordered a 2.4w front bulb, downgraded from a 3w bulb, and a 2m cable
to link the 0.6w rear light to the generator. I plugged the cable
into a socket on the B&M front light case. I ran the cable, with the
Rholoff gear cables to the rear mudguard, and through a hole to the
underside of the mudguard where it is taped to the underside (I may
superglue it later) and is run to the end of the mudguard where it
makes indirect contact with the bulb.

All would be fine and perfectly understandable if there was another
cable - but there is only one. So what happens to the electrons after
they pass through the rear bulb?

I always tell my primary school pupils that for a light to work a
circuit must be complete, and we perform endless investigations to see
if we can light a bulb with an incomplete circuit. To date, our
investigations have all been fruitless. My only thought is that
perhaps the bike's frame works as part of the circuit, but surely this
is not possible. The mudguard is plastic with metal supports,
attached to the rear rack, attached to the frame, with the front lamp
also attached to the frame. Surely the whole bike hasn't been
designed to allow it to be used as a circuit? But I can think of no
other explaination.

Can anyone enlighten me?
--

The SON dynamo does not have a connection to ground, but bicyclelights
usually do. The headlight is grounded through the mounting bolt, as is
the rearlight. Brakecables and incomplete lubrication in the headset are
usually sufficient to establish a return path for the small current.

Fitting a separate returnwire between headlight and rearlight is
recommended though for added reliability, most lights have connectors
(look for the earthsymbol) for this purpose
--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

Tom Crispin said:

but that's not the point. When the electrons encounter the resistance
of the front bulb they glow, making light - a simplistic explaination,
I know.

More accurate to say that they heat the wire filament (a lot). As a
byproduct of the heat, you get light (in the same way that an electric
cooker filament glows visibly, or a poker left in the fire glows visibly).

Quoted message said:

investigations have all been fruitless. My only thought is that
perhaps the bike's frame works as part of the circuit, but surely this
is not possible. The mudguard is plastic with metal supports,
attached to the rear rack, attached to the frame, with the front lamp
also attached to the frame. Surely the whole bike hasn't been
designed to allow it to be used as a circuit? But I can think of no
other explaination.

I suspect that you'll find that either the mudguard has a conductive
strip which is plasticised over, which (together with the stays & frame)
completes the circuit, or that the single wire is in fact double (like
earphone speakers), although that is less likely since it'd be obvious
from the connector.

R.

Ben Barker said:

Faraday's law states that: V=-Ndphi/dt

<snip>

Quoted message said:

Because the electrons are somewhere, but would rather be somewhere else

Always the same with bloody electrons. One moment you know where they
are, the next they're gone! Mostly back up the metal strip in the
mudguard, which in my experience never quite attaches to the go home
path :-(

Hmmmm...SON Dynamo <checks list> Nope, I don't have one of those...yet...

Richard said:

I suspect that you'll find that either the mudguard has a conductive
strip which is plasticised over, which (together with the stays & frame)
completes the circuit, or that the single wire is in fact double (like
earphone speakers), although that is less likely since it'd be obvious
from the connector.

Usually the rearlight bolts through the metal bracket which connects to
the metal stays.

--
---
Marten Gerritsen

INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl

Tosspot said:

Always the same with bloody electrons. One moment you know where they
are, the next they're gone!

Prof Heisenberg would disagree.

--
Tony

"The best way I know of to win an argument is to start by being in the
right."
- Lord Hailsham

Tony Raven said:

Tosspot said:

Always the same with bloody electrons. One moment you know where they
are, the next they're gone!

Prof Heisenberg would disagree.

Who are you going to believe? Tosspot or some dead prof? The good
professor never seemed very sure anyway.
John Kane, Kingston ON Canada

John_Kane said:

Quoted message said:

Quoted message said:

Always the same with bloody electrons. One moment you know where they
are, the next they're gone!

Prof Heisenberg would disagree.

Who are you going to believe? Tosspot or some dead prof? The good
professor never seemed very sure anyway. John Kane, Kingston ON Canada

I'm sure Wafflycat can lend us a feline for use in an experiment.

Tom Crispin said:

I'm not an expert at Physics - I have a B grade 'O' level. I teach basic
electrics to primary children,

As all primary schoolchildren should know:

div E = rho / epsilon0
div B = 0
curl E = - dB/dt
curl B = mu0 J + mu0 epsilon0 dD/dt

Now if they DON'T know this I suggest a long session of repetition, plus
lines for the recalcitrant.

in message <[email hidden]>, Tom Crispin

(') said:

All would be fine and perfectly understandable if there was another
cable - but there is only one. So what happens to the electrons after
they pass through the rear bulb?

The 'other cable' is the frame of the bike itself.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
Ye hypocrites! are these your pranks? To murder men and give God thanks?
Desist, for shame! Proceed no further: God won't accept your thanks for
murther
-- Roburt Burns, 'Thanksgiving For a National Victory'

Tony Raven said:

Prof Heisenberg would disagree.

Not all. You can know exactly where they are, just not what they're up
to!

Or you can find out what the sneaky buggers are doing, but not where
they're doing it.

:-)

Jon

John Hearns said:

As all primary schoolchildren should know:

div E = rho / epsilon0
div B = 0
curl E = - dB/dt
curl B = mu0 J + mu0 epsilon0 dD/dt

Now if they DON'T know this I suggest

....you send them out in search for a magnetic monopole, and tell them
not to come back until they've found it.

R.

John Hearns said:

John_Kane said:

Quoted message said:

> Always the same with bloody electrons. One moment you know where they
> are, the next they're gone!

Prof Heisenberg would disagree.

Who are you going to believe? Tosspot or some dead prof? The good
professor never seemed very sure anyway. John Kane, Kingston ON Canada

I'm sure Wafflycat can lend us a feline for use in an experiment.

She doesn't actually need to - just have one in or not in a box.

...d

Richard said:

John Hearns said:

As all primary schoolchildren should know:

div E = rho / epsilon0
div B = 0
curl E = - dB/dt
curl B = mu0 J + mu0 epsilon0 dD/dt

Now if they DON'T know this I suggest

...you send them out in search for a magnetic monopole, and tell them not
to come back until they've found it.

Dearie me. All they need to do is follow the chain of decaying protons.
All schools DO have their own proton decay experiment don't they?

John Hearns said:

As all primary schoolchildren should know:
div E = rho / epsilon0
div B = 0
curl E = - dB/dt
curl B = mu0 J + mu0 epsilon0 dD/dt
Now if they DON'T know this I suggest a long session of repetition,
plus lines for the recalcitrant.

I am 42 and don't know these, yet you expect primary children to be
taught this (the only curl("product"😉 I know is applicable to 3d vectors
[and we didn't study this till the fourth year of a thin sandwich degree
course]) have no idea what you mean by div .
--
This post contains no hidden meanings, no implications and certainly no
hidden agendas so it should be taken at face value. The wrong words
may be used this is due to my limitations with the English language .

in message <[email hidden]>, Tony Raven

(') said:

Tosspot said:

Always the same with bloody electrons. One moment you know where they
are, the next they're gone!

Prof Heisenberg would disagree.

Yeah, but I've always been a bit uncertain about him.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; no eternal reward will forgive us now for wasting the dawn.
;; Jim Morrison

Quoted message said:

I am 42 and don't know these, yet you expect primary children to be
taught this

Quoted message said:

This post contains no hidden meanings, no implications and certainly no
hidden agendas so it should be taken at face value. The wrong words
may be used this is due to my limitations with the English language .

The previous post contained irony so should not be taken at face value...
:-)

The weird thing about being English is that very occasionally we read/hear
something with no irony or self-deprecating understatement, and get
completely confused

i.e. Ask a foreigner how good he is, he might say "I'm ok".

We assume that to mean "I'm pretty good".

They actually mean "I'm ok".

Weird.

Mark Thompson said:

The previous post contained irony so should not be taken at face
value... :-)

Maybe, as usenet is a "purely" text medium and no one can see your
(TINY) face /hear your voice (TINY), a smiley would help convey the
fact that the post was ironic.
--
This post contains no hidden meanings, no implications and certainly no
hidden agendas so it should be taken at face value. The wrong words
may be used this is due to my limitations with the English language .