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

Alright, I think I might be getting there (I'm ignoring all this stuff about semi-conductors because I can't see how it pertains to sweets). Supplementary question then: If you buy a battery powered product, the cells are usually lined up in two rows. Is this more powerful in some way than having one row, or does it make no difference?

They may look as if they are lined up in two rows, but if you check the way the connections are wired up, you will find that they are nearly always electrically connected in a single line. This has the effect of adding up all the voltages, so if there are 6 batteries at 1.5 V each, then there are 9 volts available to drive the device.

You could connect the batteries in two rows of three which would give 4.5 V available, but the batteries would last twice as long as only one row of three. In general it is not done this way in battery powered devices.

Traveller in Time checking battery products
"I have a wireless mouse two cells mounted in either side, connected in series.
Flashlights: --a single cell does not add to the question. Two cells in line and in series, same circuit as the mouse.

Ah something with three cell battery all three next to each other connected in series.

Something with six cells, an Ultrasound distance measurer using a battery pack block shaped with six cells stached inside, connected in series.


Not at hand, a car battery, eight cells in a row, connected series.

The position of the battery is based on design of the device, rather then anything with the power. All devices use the cells connected in series. The width of the battery is a measure for the maximum delivered current and the weigth is a rate for the total power it can hold.


I advise _not_ to make parralel connected circuits, the cells will if not exactly identical in voltage discharge over eachother, just heating up the batteries and no benefit for the power you can use by the battery. Car batteries can even explode when connected in parralel. "

<>

Uhhh... a conductor with a non-finite resistance? Isn't that a contradiction? If it's got infinite resistance, it's an insulator.

Threads like these make me realise how hard a time mathsy and non-mathsy people can have talking to each other sometimes.

>>Uhhh... a conductor with a non-finite resistance? Isn't that a contradiction?<<

Err, yes. The deliberate mistake in my post was the inclusion of the word "non"

Is non a word (in English) ?

No, it's a proper noun...

Non - p. noun - cohort of General Zod

Presumably most things that are insulators are semiconductors with a very large band-gap? The definition of "very large" is presumably arbitrary and depends on the application?

A material can conduct only if the electrons, normally bound to the atoms in the material, can be promoted to a 'conduction [energy] band', in which they are physically free to move throughout the material... The difference between the 'rest', bound electrons, and the minimum energy of the conduction band, is the 'band-gap'. (Sort of).

As far as I understand:
- A metal is a material with zero band gap
- A small-band-gap semiconductor is a material with a finite band gap which is easily overcome by natural thermal energy (ie, the ambient temperature makes it effectively metallic)
- A semi-conductor is everything else, in which external energy (ie, from an electric field) is needed to excite electrons into the conduction band (and overcome the band-gap)
- An insulator is something with a very big band-gap

I was unsure as to what Breakdown voltage means... According to the other place, "breakdown voltage" is the voltage at which you may promote electrons in a insulator to the conduction band; "dielectric breakdown" is when you apply so large an electric field that the structure of the material is modified in some way to allow conduction.

"What's the difference between and volts, amps and watts?"

Formally:

Amps are the units of electric current, which is a flow (movement) of charge past a point.
Electric current would usually be a flow of electrons (which have charge).

<< The current is defined as the amount of charge which crosses a point in unit time. >>

So if the charge is measured in units of Coulombs (one electron carries a charge of 1.6 x 10^-19 Coulombs), the current, in amps, is the charge, in Coulombs, which crosses a point in a circuit every second. Or, another way, if you divide the current by the electron charge, that will tell you how many electrons are crossing a point in a circuit every second.

<< Voltage is the work done in transferring a unit charge between two points in a circuit. >>

So it is the energy (in SI units, Joules) lost by the electrical circuit in transfering one Coulomb of charge between two points in a circuit. If the two points happen to lie either side of a light bulb, for example, then a lot of that lost energy goes into making the light bulb illuminate (and heat up!).

Watts are the units of power, which is, in general, a measure of the rate at which energy is consumed/used/provided (ie, by an electric circuit). So, in SI units, 1 Watt = 1 Joule used per second.

Note, this waffle can be expressed as:
[Current] = [Charge] / [Time]
[Voltage] = [Energy] / [Charge]
[Power] = [Energy] / [Time]

You can see from rearranging these fractions that [power] = [Energy] / [Time] = ([Energy] / [Charge]) * ([Charge] / [Time]) = [Voltage] * [Current]

So, [power] = [voltage] * [current]

Power is measured in units of Watts
Voltage is measured in units of Volts
Current is measured in units of Amps