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Original poster

Can you explain electricity to me, please?

53 replies

roisin · 20/10/2005 21:00

I have vague memories of a physics teacher talking about ping pong balls, and it just never made sense to me.

Now I've got ds1 banging on about atoms and electrons, and I still don't get it.

OP posts:
Nightynight · 20/10/2005 21:24

electrons are small negatively charged particles that revolve around the nucleus of an atom.

when you apply a potential difference between 2 ends of a copper wire (a voltage), the electrons feel an uncontrollable urge towards the positive end. so they get pulled of their atom and onto the next one. that's current flow.

Actually, Im lying a bit - most of current flow is just energy passed on when the electrons get all excited and bang into things. they dont actually physically move very far.

Nightynight · 20/10/2005 21:26

does that help?

better ask martianbishop, she's a physics teacher!

Original poster
roisin · 20/10/2005 21:30

OOh thank you! I thought I was going to fall off the list with no replies!

So is the electricity the 'excitement' of the electrons?

So the electricity is IN the atoms of the copper, say. And can get passed on to be IN the atoms of, say, a piece of iron?

So why do some materials not conduct electricity?

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Blandmum · 20/10/2005 21:30

Current is the flow of electrons. When you apply a potential difference to a wire the free electrons move (think of them being like a fog of electrons that gets 'blown' by the potential difference) Current alawys stays the same, because the electrons never leave the wire. What the battery or the power pack gives to the electrons is energy. This energy is used up by the items in a circuit, say a light bulb. Inside a light bulb the electrons give up their electrical enengy and it is converted to light (and heat) energy). the energy carried by the electrons is the voltage.

So when the electron pass through the battery they pick up enegy, which is then converted to other forms of enegy by the things in the circuit. Current always stays the same in the circuit, voltage is measiured across the items in a circuit, it measured what is 'used up'

Blandmum · 20/10/2005 21:31

Biologist! But I do teach this to the lower school. In reality it is quite a bit more complex than this!

hunkerpumpkin · 20/10/2005 21:32

It's magical fluid that comes out of plugs. They need to be turned off if they've got nothing plugged into them, or it leaks out and makes the hairs on your toes crackle (I'm a hobbit).

Blandmum · 20/10/2005 21:33

Roisin, excellent questions!

In a metal the electrons are in the 'cloud' that I mentioned before. the positive centers of the atoms don't attract them too stongly. In insulatore the electons are stronly attracted to the positive middle bit of the atoms and are not as free to move.

Original poster
roisin · 20/10/2005 21:33

Please don't make it more complicated! I think I'm beginning to get somewhere

You both used the term 'potential difference' ... What does it mean?

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JoolsToo · 20/10/2005 21:33

yes - there are little white square all over your house - the ones high up on the wall you press and a light comes on - providing the bulb hasn't gone. The ones near the floor have little holes in that you push a plug into for all sorts of things like watching telly, doing the ironing or drying your hair.

Other than that I haven't the foggiest idea!

JoolsToo · 20/10/2005 21:34

oh yes! and there's the other electricity - like when you touch someone you fancy

hunkerpumpkin · 20/10/2005 21:34

JT, you're as scientific as me! LOL!

startingtobehalloweenylover · 20/10/2005 21:34

what's a potential difference?

Original poster
roisin · 20/10/2005 21:36

JT - the "little white squares" explanation has always sufficed for me. But I have this illogical desire that I should be able to understand anything ds1 does (except Star Wars and Gameboys) until he's at least 11

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JoolsToo · 20/10/2005 21:40

dh is the scientist/mathematician in our house - I'm better at english/art/practical stuff.

Science is like Chinese to me! I wish you luck!

Blandmum · 20/10/2005 21:42

OK, we now move from ks3 to ks4!

Potential difference can be used in lots of different areas of physics, In this case it relates to the amount of enegy that is transfered from one part of a circuit to another. It is measured in volts....aka the voltage. So if you are stil looking at a light bulb it is the difference between the amount of energy present in the electrons on one side to the other (the difference being the enegy that has been converted into light and heat enegy)

The voltage (potential difference) across the battery is what 'pushes' the elecrons round the circuit.

And analogy would be your central heating system. The electrons are represented by the water in the pipes. You don't loose the water from your systen....this is the current and it stays the same all round the system. The pump/heater is what causes the water to gain energy (get hotter) and move rounds the system. (this is the battery). As the water passes through a radiator there is a difference in the energy in the water from one side of the radiatoir to the other, as heat enegy radiates out. There is a porential difference across the radiator.

Phew, physics after 9!

startingtobehalloweenylover · 20/10/2005 21:45

ahhh i "think" i get it

gosh, mumsnet teaches me all kinds of things!

Original poster
roisin · 20/10/2005 21:46

So if I built a circuit with a battery but no bulb (or other energy-using thing), would the electricity not flow? Or have I misunderstood something?

OP posts:
Nightynight · 20/10/2005 21:52

small amounts of energy get used in the wires of the circuit, so yes, current would flow.

startingtobehalloweenylover · 20/10/2005 21:52

yeah it would just go round and round

wouldn't it?

Blandmum · 20/10/2005 21:52

Yes it will flow, there are two potential differences to think about, across something like a bulb, but also across the battery itself.

Inside the battery a cemical reaction happens, converst stored chemical enegy to electrical energy which is 'given' to the electrons.

Some energy is lost in the wire itself.....wires heat up as electrical energy is converted to heat energy....this is what happens in an electrical 'bar' heater. Think of it like water frowing down a mountain from there there is a lot of potential energy, at the top of the hill (gravitational in this case) to where there is least, at the bottom of the hill

Blandmum · 20/10/2005 21:53

And eventually the cemical reaction in the battery stops (runs out of chemicals basicaly) so it can no longer generate the electrical energy to cause the potential difference.

Original poster
roisin · 20/10/2005 21:56

OK, I'm getting brainache now. I think I need to go and assimilate all this information!
Thank you Nightynight and Martianbishop

PS This is all ds1's fault. He came home from school delighted that he'd got full marks in an electricity test, but disappointed there had been no questions about atoms and electrons! (He's 8!)

OP posts:
Blandmum · 20/10/2005 21:57

Sorry I couldn't make it any easier....I'm a biologist!

Nightynight · 20/10/2005 21:58

wow, congratulations to ds!

Original poster
roisin · 20/10/2005 22:00

I thought you were a chemist, I don't know why!

PS I still haven't found a milkbottle to do the egg thing. But hope to do so soon!

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