h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

With all respect Gnomon - please correct me if I am wrong - but:

Electricity is a phenomenon and not energy. If electricity was energy its unit should be joule. I never heard anybody say 'this battery has an electricity of 20 J.'

Maybe both terms are too fuzzily defined. Electricity being the movement of charge and energy the capability of something to do work. Interrelated yes, but the same - I say no.

I wouldn't also leave this in the Entry on the grounds that 'most people' think electricity is a form of Energy. You see? 'Most people' believe the strangest things. This Entry should explain what Electricity is, and not confuse matters even more. I think the best thing is to avoid this sentece ('Electricity is a form of energy').

Just my 2p.

HELL

I think VoltAmps are beyond the scope of this entry. Stick to watts for measuring power, because they are the standard unit of power.

Power is the rate of change of energy, the rate at which the energy is used up or provided. So it is joules per second. It is only slightly incorrect to say that power is energy per second, since the second is the standard unit of time.

In the non-scientific use of the term energy in English, electricity, oil, gas and coal are all forms of energy. Obviously in scientific language coal is not energy, it is matter, but that is one of the normal uses of the word energy.

It might be worth saying that electricity is strictly speaking a method of getting energy from one place to another, rather than being energy itself.

Hi Gnomon,

I'm happy with that! "It's only slightly incorrect...".

I agree that KVA and power factor are out of scope, but I wanted to explain the difference. They are not the same.

I also agree with HELL. The author has taken on a complex and abstract subject and we don't want to add to any existing misconceptions or un-truths.

Awu.

I only mention lightning because some early experiments on electricity were done using a kite, a key and a thunderstorm (don't try it at home).

If you are writing about the fundamentals of electricity, one of the basic facts is that for a current to flow requires a circuit - flow and return. (People might be wondering why birds are not electrocuted when perching on high-tension wires.) So when you talk about direction of flow, you need to factor this in.

Returning to the semiconductor bit,

Gnomon's comment, "the thing that makes them semiconductors is not that they change resistance with temperature, it is that they conduct slightly." isn't really true.

Defining what a semiconductor is, is not easy. Semiconductors are characterised by a relatively small energy gap between the conduction band and the (completely filled) valence band. At zero kelvin they act as insulators but as the temperature rises electrons are thermally excited into the conduction band and the resistance falls. But the resistance depends more critically on the concentrations of impurities in the sample. (follow that )

The entry the author linked to explains this is more detail. I can understand why he/she says "You don't need to think about this unless you have a PhD in Life, the Universe and Everything", but if this were true we wouldn't have any modern computers or electrons.

Maybe a better sentence would be, 'semiconductors are materials which can behave as both conductors or inductance, they allow the flow of current to be controlled making them an essential part of modern electronics' or something like that.

MP

The light bulb was invented by Thomas Edison AND Sir Joseph Swan; it's just that Edison got the lion's share of the credit.

Hi,

this is not easy to explain in one sentence!
Actually the basic material (usually silicon) doesn't conduct. But when it's doped with arsenic or boron it becomes a semi-conductor. The real magic happens at the junction of the negatively (N) or positively (P) doped material.

How about...

'...they allow the flow of current to be controlled across the junction of two types of semiconductor material, making them an essential part of modern electronics'

Awu

... in case anyone cares.

The "valency gap" that MP talked about is due to the fact that the doping elements have a valency one higher or lower than that of silicon. This results in a derth or glut of free electrons.

Awu.

Waitwaitwait... Silicon IS a semiconductor.

Doping just makes it a little less 'semi-conductor' and more 'conductor' (so that the stuff can work on room temp, and so that one knows from where to where the electrons are hopping. The dope brings the (aformentioned) bands closer. Silicon is also a semiconductor even without the dope.

HELL

There's no harm in mentioning that semiconductors are the basis for electronics, but an entry like this should not start talking about doping, valency or p-n junctions. It's supposed to be about electricity in general, not electronics in particular.

Please STOP talking about semiconductors. There are other guide entries which talk about this in great detail.

We'll stop talking about them when we're happy with the reference to them in your entry!

At present, it says: "In addition there are Semiconductors, which is something with a resistance that goes down as it gets hotter. You don't need to think about this unless you have a PhD in Life, the Universe and Everything."

I'm happy with the description of their resistance, but I think the comment about the PhD suggests they are more complex than they really are. Any undergraduate course in electronics requires an understanding of semiconductors. I'd be happy if you changed 'PhD' to 'degree'.

In light of how much there is about electricity, i've changed the remit of the entry from:
"Everything you never wanted to know about Electricity"
to:
"Not quite everything you never wanted to know about Electricity, but quite a lot of it"
Perhaps this will discorage you from picking too many holes in it (though probably not)

It's a great entry, Bob!

But you'll have to put up with us picking holes in it if you want it to get through Peer Review.

You're right. Probably not .

I was not picking a 'hole' - i.e. something you might have omitted. I am quite OK with the scope of this Entry - you might even consider EXCLUDING some bits, so that you don't have to go too deep into details. I was being nitpicky about stuff that is in there already. In my view there are some passages - such as the one stating that electricity is energy - which could be formulated differently, so not to cause confusion. E.g. something along the lines of: 'Like coal and oil, electricity is regarded as a form of energy...' would settle this matter for me.

HELL

Hi Bob,

Sorry - I didn't mean to pick holes either. And I wasn't suggesting that anything I wrote should get included.
But to be able to make a passing reference to something like Semiconductors or KVA you need quite a bit of background. You have to pare it own to a sentence or two but still keep it accurate. I think we were just trying to give you some more info. to do that.

My German teacher used to say (about writing exams.) "If you can't say it, don't say it"


HELL,
I agree that materials like Silicon (and copper oxide or whatever the others are) are semiconductors. But when we talk about the semiconductor industry, or technology, I think we mean building and manipulating the doped varieties. You can't build even a diode without them.

Awu

You might find the following distinction useful:
The *conductivity* measured in Siemens/cm (a Siemen is a reciprocal ohm) of a solid is the product of the concentration of charge carriers multiplied by their mobility (their velocity per unit applied field). Mobility in solids tends to decrease as temperature goes up as lattice virbrations interfere increasingly with the free flow of charge carriers.

In metals, the number of free charge carriers (electrons) remains constant with temperature and hence conductivity is governed by changes in mobility. However, in semiconductors, Boltzmann's law sees a huge increase in the number of charge carriers as the temperature increases, swamping any mobility-related effects.

So I suppose that what I am saying is that if you want to talk about semiconductors, you're probably going to have to get your hands dirty and delve into all this mucky stuff. Good luck: you'll need it!

FM

I think that you don't need semiconductors to explain the phenomenon of electricity. It would be easier and clearer if you left that part out.

HELL