# Physics - GCSE electricity

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#1
Ok, we've just finished a module on electricity and quite honestly I don't understand a thing. Neither can a lot of girls funnily enough. I understand biology and chemistry but...physics! No no!

So anyway, I need a bit of help. The module consists of :

• Coil
• Farrarday's left hand thing
• Voltage, Amps and Ohms
• Transformers - actually I understand that and ONLY that
• Static electricity
• Dust precipitator

I'd be very grateful if anyone would kindly help me a bit with any of these topics.

Thank you very much!

~Gemma~
0
18 years ago
#2
(Original post by gemgems89)
Farrarday's left hand thing
Do you mean Fleming's left hand rule? If so, you use it when a conductor is moving in a magnetic field. Your thumb, first finger and second finger should be at right angles to each other.

thuMb - motion (the direction of motion of the conductor)
First finger - field (the direction of the magnetic field, north to south)
seCond finger - current (the direction of the current. This is conventional current, so positive to negative)

Hope that makes some sense.
0
18 years ago
#3
Erm, first the coil

Well do you understand how a magnetic field is created around a single wire, for a start? It's like a corkscrew... if the current is flowing away from you, the magnetic field goes clockwise (in a circle around the wire) but if the current flows towards you the current flows anti-clockwise.

So when it gets bent into a coil, as you can imagine the magnetic field lines would be very similar to for a bar magnet. You need a diagram to show it really, I'm sorry.

Btw- It's Fleming's left hand rule. It's to do with the motor effect.

I'd help more but I'm not the best in the world at explaining things, especially in text.
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18 years ago
#4
(Original post by Nylex)
Do you mean Fleming's left hand rule? If so, you use it when a conductor is moving in a magnetic field. Your thumb, first finger and second finger should be at right angles to each other.

thuMb - motion (the direction of motion of the conductor)
First finger - field (the direction of the magnetic field, north to south)
seCond finger - current (the direction of the current. This is conventional current, so positive to negative)

Hope that makes some sense.
Yeah, Fleming's Left Hand rule is in the GCSE specification.

For the benefit of Gemma, this refers to how the conductor moves when a current is passed through it across a magnetic field. For example, if you have a wire passing between the N and S poles of a magnet and you pass a current through the wire, the wire will move.
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18 years ago
#5
You'll also induce an EMF (and therefore a current, if it's a closed circuit) in the wire if you simply move it up and down through the magnetic field (was what I meant, soz it wasn't clear).
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18 years ago
#6
(Original post by Nylex)
You'll also induce an EMF (and therefore a current, if it's a closed circuit) in the wire if you simply move it up and down through the magnetic field (was what I meant, soz it wasn't clear).
Yes, the dynamo effect.

I find it interesting that Gems needs to know about generators but not Fleming's Right Hand Rule. It's pretty important to help you understand it, just like the Left Hand Rule is useful in understanding electric motors.
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18 years ago
#7
Alright, if no-one else is gonna help...

Static electricity

You rub two things together. Electrons transfer from one to the other. The one where all the electrons gather are negatively charged, because as you know before each proton would have had an electron to cancel out its charge so every atom would be neutral. So now there are more electrons than protons so there is negative charge. Where the electrons moved from has lost electrons, so there are more protons than electrons so it is positively charged.

Positive and Negatively charged matter attract each other - it's a law of electrostatics. So the two things will attract each other.

A positively charged rod will attract to neutral objects though. That's because the positive rod attracts more electrons in the neutral object towards the side closest to it, so that side becomes negatively charged which makes it attract even more, so the whole thing attracts towards the rod. A negatively charged rod encourages electrons to repel to the other side of the neutral object, making the nearer side of it positively charged so it attracts to the rod again.

I think I've got that right. Diagrams are helpful in explaining this.
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#8
(Original post by Nylex)
Do you mean Fleming's left hand rule? If so, you use it when a conductor is moving in a magnetic field. Your thumb, first finger and second finger should be at right angles to each other.

thuMb - motion (the direction of motion of the conductor)
First finger - field (the direction of the magnetic field, north to south)
seCond finger - current (the direction of the current. This is conventional current, so positive to negative)

Hope that makes some sense.
Yes, that's what I meant. Thank you!

(Original post by mik1a)
volts amps and ohms is an easy one and I can't say I've learnt many others so :

basically you need Ohm's law to work these out:

V=IR

which states that the voltage across a resistor is equal to the current across the resistor times the resistance generated by the resistor.

in a series circuit the current is always the same wherever you are, so if you have a 5A circuit with a 5(ohm) resistor, the voltage across it will be 15V.

to remember the equation, just remember that Voltage is on the top of the triangle. so to work out resistance, voltage is over current. (R=V/I), and to work out the current, the Voltage is always over the resistance (I=V/R)

You can practice these with millions of questions, just give urself randomly generated numbers of volts, ohms and amps and try to work out the third one from the first two.
Yes, I think I know the equations. The trouble is when I get shown a circuit with lamps in and it asks whether the voltage starts off low and then rises to a steady pace. Things like that.

(Original post by thefish_uk)
Alright, if no-one else is gonna help...

Static electricity

You rub two things together. Electrons transfer from one to the other. The one where all the electrons gather are negatively charged, because as you know before each proton would have had an electron to cancel out its charge so every atom would be neutral. So now there are more electrons than protons so there is negative charge. Where the electrons moved from has lost electrons, so there are more protons than electrons so it is positively charged.

Positive and Negatively charged matter attract each other - it's a law of electrostatics. So the two things will attract each other.

A positively charged rod will attract to neutral objects though. That's because the positive rod attracts more electrons in the neutral object towards the side closest to it, so that side becomes negatively charged which makes it attract even more, so the whole thing attracts towards the rod. A negatively charged rod encourages electrons to repel to the other side of the neutral object, making the nearer side of it positively charged so it attracts to the rod again.

I think I've got that right. Diagrams are helpful in explaining this.
Yes, I was reading up on it all last time and now I understand.

Thanks for all your help too.

Does anyone know about the dust/smoke precipitator?
0
18 years ago
#9
(Original post by gemgems89)
Does anyone know about the dust/smoke precipitator?
Ahhh.... I wrote all this out on a message last night and the server was busy, lol.

Basically... metal plates in the chimney (in the case of smoke) are connected to a power supply which makes them charged. This attracts the dust and smoke particles to them. An automated moving device, I think, automatically knocks the collected dust off them so it can be disposed of.

Ionisers are slightly different. They are little boxes with holes in that you can put in rooms and they clear the air of dust, by ionising the air and the dust particles causing them to attract to surfaces. I know this because I used to have one in my bedroom and the dust it attracted made a mess on the ceiling.
0
18 years ago
#10
(Original post by gemgems89)
Yes, that's what I meant. Thank you!
No prob .
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