what direction does a current flow in the current?

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#1
what direction does the current and or electrons flow in a circuit ?

is it positive to negative

or negative to positive?

"Current flows from the positive (+ve) terminal of the battery to the negative (-ve). This is called conventional current flow. The problem is, electrons are negatively charged, so they want to get away from the -ve and go to the +ve. So if electrons are going left to right, you say that the current is going right to left (how confusing is that!)"

can anyone decode the above jargon please?

ty
1
8 years ago
#2
Electrons in a circuit travel from the negative terminal to the positive. (Repelled by the - and attracted by the +)
Unfortunately, in the early days when much of the theory of current electricity was formulated (Ohm's Law etc) the electron hadn't been discovered. So when they indicated the direction of current they showed it going from positive to negative. It was a guess. They got it wrong. This is called "conventional" current. So in circuit diagrams you usually show "conventional" current as going from + to -. You also sit back and think, ah yes, but the electrons are actually going the other way. In the long term it doesn't really matter so long as you understand what's going on and why.
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#3
(Original post by Stonebridge)
Electrons in a circuit travel from the negative terminal to the positive. (Repelled by the - and attracted by the +)
Unfortunately, in the early days when much of the theory of current electricity was formulated (Ohm's Law etc) the electron hadn't been discovered. So when they indicated the direction of current they showed it going from positive to negative. It was a guess. They got it wrong. This is called "conventional" current. So in circuit diagrams you usually show "conventional" current as going from + to -. You also sit back and think, ah yes, but the electrons are actually going the other way. In the long term it doesn't really matter so long as you understand what's going on and why.

so in a circuit, i have to show wrong direction a current flows?

mind has been blown.

thank you for your constant informative replies on these forums.
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8 years ago
#4
(Original post by medicine gapper)
so in a circuit, i have to show wrong direction a current flows?

mind has been blown.

thank you for your constant informative replies on these forums.
In most electrical circuits (the sort you do calculations on) you show conventional (positive) current. To say it's "wrong" is to misunderstand. The arrow in the circuit doesn't claim to show the direction of electrons. It's just current. When that current meets a junction and divides, it shows the two currents formed. You can then calculate these two currents. You will still get the right answer, whether or not the current is positive or negative. In fact, the current in some circuits and materials can be positive. A beam of protons or alpha particles is positive current. In an electrolyte, positive ions flow one way and negative ions the other way. In metals it's electrons that flow. You have to choose one direction for current. Positive was chosen many years ago and that's what we use today. You need to keep to this convention because there are many rules which use it. If you have studied Fleming's Left Hand Rule, for example, you will know what I mean. If not you have that pleasure awaiting you.
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#5
(Original post by Stonebridge)
In most electrical circuits (the sort you do calculations on) you show conventional (positive) current. To say it's "wrong" is to misunderstand. The arrow in the circuit doesn't claim to show the direction of electrons. It's just current. When that current meets a junction and divides, it shows the two currents formed. You can then calculate these two currents. You will still get the right answer, whether or not the current is positive or negative. In fact, the current in some circuits and materials can be positive. A beam of protons or alpha particles is positive current. In an electrolyte, positive ions flow one way and negative ions the other way. In metals it's electrons that flow. You have to choose one direction for current. Positive was chosen many years ago and that's what we use today. You need to keep to this convention because there are many rules which use it. If you have studied Fleming's Left Hand Rule, for example, you will know what I mean. If not you have that pleasure awaiting you.
just to relate this to another concept

http://www.s-cool.co.uk/gcse/physics...ectromagnetism

"If the conventional current flows the other way, the magnetic field will be in the opposite direction. As you move further away from the wire, the magnetic field gets weaker, which is why the lines are drawn further apart.These types of magnets are called electromagnets. They are temporary magnets as they can be turned on and off with the current. Normal bar magnets are permanent magnets because it is very difficult for them to lose their magnetism."

Electrons flowing through a wire produce a magnetic field. electrons flowing through a coiled wire produce a different kind of field.

what i wish to unders.tand is...why does it say, electrons flowing opposite to the convectional current in a wire...produce electro magnets? i don't understand this at all
0
8 years ago
#6
In reality they flow from negative to positive.

However, in all diagrams they are presumed to flow from positive to negative. This because people used to think this was the case and when they found out it wasn't true they just continued using the old conventional system for ease.
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8 years ago
#7
It's the same sort of field for a wire as a for a coil of wire.
When it's coiled the fields in each turn add together to make a stronger field.

Electrons being negatively charged and moving in the opposite direction to the current is just something you need to remember.
If you're looking at currents and charges it doesn't make any difference if the charge carriers were positively charged and moving with velocity +v or negatively charged and travelling with velority -v. The movement of charge (which is what we're interested in) would be identical.
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8 years ago
#8
(Original post by medicine gapper)
just to relate this to another concept

http://www.s-cool.co.uk/gcse/physics...ectromagnetism

"If the conventional current flows the other way, the magnetic field will be in the opposite direction. As you move further away from the wire, the magnetic field gets weaker, which is why the lines are drawn further apart.These types of magnets are called electromagnets. They are temporary magnets as they can be turned on and off with the current. Normal bar magnets are permanent magnets because it is very difficult for them to lose their magnetism."

Electrons flowing through a wire produce a magnetic field. electrons flowing through a coiled wire produce a different kind of field.

what i wish to unders.tand is...why does it say, electrons flowing opposite to the convectional current in a wire...produce electro magnets? i don't understand this at all
I think you are "over-thinking" all this.
The theory for electromagnets (the direction of the magnetic field etc) was formulated before the discovery of the electron. It is all based on the idea of conventional current. The diagrams and rules all use this conventional current.
You ask why it says "electrons flowing opposite to the conventional current". Have I not already explained this. Conventional current is defined this way. It's a definition. You will get a magnetic field if protons move through space. Any charge can produce a magnetic field if it moves.
If you connect a battery to a circuit the battery has a positive and a negative terminal. By convention, you show the current flowing from plus to minus.
You can understand the whole of "current electricity" without ever knowing what is actually flowing in the wire. When a current flows in a wire, a magnetic field is created. That's all there is to it. If you want to know the direction (North South etc) of the field you need to know the direction of the conventional current. So if you have connected a battery with a plus and minus terminal, you know which way the conventional current is flowing. You then know the direction of the field.

It would be better to post some exam questions on this topic here and discuss them, and the answers, rather than bang on about this bit of theory.
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#9
(Original post by Stonebridge)
I think you are "over-thinking" all this.
The theory for electromagnets (the direction of the magnetic field etc) was formulated before the discovery of the electron. It is all based on the idea of conventional current. The diagrams and rules all use this conventional current.
You ask why it says "electrons flowing opposite to the conventional current". Have I not already explained this. Conventional current is defined this way. It's a definition. You will get a magnetic field if protons move through space. Any charge can produce a magnetic field if it moves.
If you connect a battery to a circuit the battery has a positive and a negative terminal. By convention, you show the current flowing from plus to minus.
You can understand the whole of "current electricity" without ever knowing what is actually flowing in the wire. When a current flows in a wire, a magnetic field is created. That's all there is to it. If you want to know the direction (North South etc) of the field you need to know the direction of the conventional current. So if you have connected a battery with a plus and minus terminal, you know which way the conventional current is flowing. You then know the direction of the field.
ahh , yes i understand.

a current flows through a wire = magnetic field forms.

however, if i wanted to know what direction the current is going in...do i use the convectional current, or the actual direction currents go in (negative to positive?)
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8 years ago
#10
This is something that pisses me off too actually. I study Electrical Engineering, and it's just something that annoys me, but I just accept it.
0
8 years ago
#11
(Original post by Stonebridge)
I think you are "over-thinking" all this.
The theory for electromagnets (the direction of the magnetic field etc) was formulated before the discovery of the electron. It is all based on the idea of conventional current. The diagrams and rules all use this conventional current.
You ask why it says "electrons flowing opposite to the conventional current". Have I not already explained this. Conventional current is defined this way. It's a definition. You will get a magnetic field if protons move through space. Any charge can produce a magnetic field if it moves.
If you connect a battery to a circuit the battery has a positive and a negative terminal. By convention, you show the current flowing from plus to minus.
You can understand the whole of "current electricity" without ever knowing what is actually flowing in the wire. When a current flows in a wire, a magnetic field is created. That's all there is to it. If you want to know the direction (North South etc) of the field you need to know the direction of the conventional current. So if you have connected a battery with a plus and minus terminal, you know which way the conventional current is flowing. You then know the direction of the field.
Since we are on the topic of electricity can you help me with some thing?

We where doing capacitors and circuits. We made a circuit with a resistor, power supply of 6v, capacitor of 1micro Farad(or 1 Farad can't remember) so anyway when we did the experiment my physics teacher said the current decreases due to the resistor in the circuit causing the (current reading being measured from the capacitor to lower down quickly over a certain time) then the voltage started from 0 and began to increase until it reached 6v? Why does the voltage increase? Is this to do with the ohms law equations R=V/I ? Also i dont understand why the capacitor reading goes to zero when you "discharge" it? Is this because all the free electrons are transferred somewhere else?

Thanks
0
8 years ago
#12
(Original post by medicine gapper)
ahh , yes i understand.

a current flows through a wire = magnetic field forms.

however, if i wanted to know what direction the current is going in...do i use the convectional current, or the actual direction currents go in (negative to positive?)
If you want to know the direction of a magnetic field caused by a current you have to use conventional current.
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8 years ago
#13
(Original post by a10)
Since we are on the topic of electricity can you help me with some thing?

We where doing capacitors and circuits. We made a circuit with a resistor, power supply of 6v, capacitor of 1micro Farad(or 1 Farad can't remember) so anyway when we did the experiment my physics teacher said the current decreases due to the resistor in the circuit causing the (current reading being measured from the capacitor to lower down quickly over a certain time) then the voltage started from 0 and began to increase until it reached 6v? Why does the voltage increase? Is this to do with the ohms law equations R=V/I ? Also i dont understand why the capacitor reading goes to zero when you "discharge" it? Is this because all the free electrons are transferred somewhere else?

Thanks
This needs to be in its own thread. I've started a new one for you.
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#14
(Original post by Stonebridge)
If you want to know the direction of a magnetic field caused by a current you have to use conventional current.
ty

so say we drew a curcuit diagram, and in this diagram we had a LED, light emitting diode, only allowing electrons or current to flow through it in one way.

we would show it going from positive - negative ?

so if the diode faced the positive, the curcuit could not work, as current is only allowed to flow ONE way across it a LED

ty
0
8 years ago
#15
(Original post by Stonebridge)
This needs to be in its own thread. I've started a new one for you.
thank you.
0
8 years ago
#16
(Original post by medicine gapper)
ty

so say we drew a curcuit diagram, and in this diagram we had a LED, light emitting diode, only allowing electrons or current to flow through it in one way.

we would show it going from positive - negative ?

so if the diode faced the positive, the curcuit could not work, as current is only allowed to flow ONE way across it a LED

ty
In a circuit, the symbol for a diode shows the direction of the conventional current that can flow through it. It points in the direction of the conventional current. As I said before, circuit diagrams and circuit theory use conventional current.
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#17
(Original post by Stonebridge)
In a circuit, the symbol for a diode shows the direction of the conventional current that can flow through it. It points in the direction of the conventional current. As I said before, circuit diagrams and circuit theory use conventional current.
for a BMAT question, they purposefully showed two diagrams, one with a diode in the direction of the convectional current, the other with the diode against.

so in a curcuit, the current flows from positive to negative.

i.e the larger side of the battery symbol to the smaller

or, in other terms, from left to right.

ty
0
8 years ago
#18
(Original post by medicine gapper)
for a BMAT question, they purposefully showed two diagrams, one with a diode in the direction of the convectional current, the other with the diode against.

so in a curcuit, the current flows from positive to negative.

i.e the larger side of the battery symbol to the smaller

or, in other terms, from left to right.

ty
Yes but forget "left to right" because the diagram can be any way around.

This shows what I mean.

On the right the (conventional) current flows clockwise round the circuit. Lamp lit.
On the left there will be no current as the diode is "reverse biased". Lamp not lit.
0
8 years ago
#19
(Original post by medicine gapper)
ahh , yes i understand.

a current flows through a wire = magnetic field forms.

however, if i wanted to know what direction the current is going in...do i use the convectional current, or the actual direction currents go in (negative to positive?)
conventional current
0
3 years ago
#20
visit http://ibiblio.org/kuphaldt/electricCircuits/ and select Chapter 1: BASIC CONCEPTS OF ELECTRICITY, search for

"CONVENTIONAL VERSUS ELECTRON FLOW"
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