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gangsta316
But isn't the thumb the force? And isn't the force the centripetal force? I'm sure I've seen a PHY6 question before with electrons going round in a bubble chamber and you had to explain why the magnetic field was in a certain direction. The answer was to use Fleming's left hand rule with the current in the opposite direction that the electrons were being fired and the force as the centripetal force.


Yeah thats the LHR though.

Induction involves the Right Hand Rule, and the thumb is direction of motion, or force. Always. Centripetal force is always the result of something else (gravitation, electrical attraction, friction etc), and it wont be used in bicycle questions.
At each spoke, you can determine that the current is going away from the centre hub, towards the rim. If the rim was negative, the electrons would repel and go to the centre, so the rim is positive and the electrons move to the outside as you would have shown with the right hand rule.
Therefore, as stated in mark scheme, hub is negative and rim is positive.

The force is in the direction of motion.
Reply 22
So to solve induction questions we need to use Flemming's RIGHT hand rule and for other examples where a resultant force is produced we need to use the left hand rule?
SimonM
Fleming's right hand rule does not involve a force:


That's queer. Does Fleming's left hand rule involve a force or is the thumb the motion, rather than the force? I use the acronym FBI to remember it so that's why I always think of it as force.
Reply 24
gangsta316
That's queer. Does Fleming's left hand rule involve a force or is the thumb the motion, rather than the force? I use the acronym FBI to remember it so that's why I always think of it as force.


Yes; thumb is force in his left hand rule
Reply 25
SimonM
Yes; thumb is force his left hand rule


I swear I have seen many questions where there is a motion of an electron in a magnetic field, so where is the force here and how do we know we have to use the left hand rule as opposed to the right?
SimonM
Yes; thumb is force his left hand rule


Thanks. I didn't know that. So with an electron going round in a circle can we use the left hand rule with the thumb as the centripetal force?

Why does the right hand rule not involve force? It sort of makes sense though because you could move a magnet through a coil with constant speed and induce a current.
Reply 27
djpailo
I swear I have seen many questions where there is a motion of an electron in a magnetic field, so where is the force here and how do we know we have to use the left hand rule as opposed to the right?


motion of an electron is a current so we can use Fleming's left hand rule to find the force acting on the electron

gangsta316
Why does the right hand rule not involve force? It sort of makes sense though because you could move a magnet through a coil with constant speed and induce a current.


The right hand rule is about motion and how it can induce a current. Motion (at a constant speed) does not need a force.
I don't get this, did this q before as well.

We are inducing an EMF with movement in a magnetic field, so thats generation, right hand rule.....

Where does the left hand come into it?
Reply 29
doggyfizzel
I don't get this, did this q before as well.

We are inducing an EMF with movement in a magnetic field, so thats generation, right hand rule.....

Where does the left hand come into it?


It doesn't. The first few posters were confused, and it seems to have had an effect on the rest of the thread.
Reply 30
you have to use right hand - it even says so in the examiner's report
SimonM
It doesn't. The first few posters were confused, and it seems to have had an effect on the rest of the thread.

Ok so that leaves the current finger pointing towards the outer part so the electrons will go towards the inter part, meaning it is negative...??
I don't remember seeing anything about Fleming's Right Hand Rule on the UNIT 5 syllabus ... It seems they just felt like dropping that lil suprise to get our heart's racing.
am I wrong?

hopefully in tomorow's exam if a question like this comes up it will only be worth one mark. :biggrin:


+++I find that compared to other boards Edexcel insists on asking the most ambiguous, quirky and downright confusing questions. At times it seems like they're trying to catch you out or like the question has been translated from another language and the wording is all off.

Thank the LORD for UMS.
Windsprite
I don't remember seeing anything about Fleming's Right Hand Rule on the UNIT 5 syllabus ... It seems they just felt like dropping that lil suprise to get our heart's racing.
am I wrong?

hopefully in tomorow's exam if a question like this comes up it will only be worth one mark. :biggrin:

+++I find that compared to other boards Edexcel insists on asking the most ambiguous, quirky and downright confusing questions. At times it seems like they're trying to catch you out or like the question has been translated from another language and the wording is all off.

Thank the LORD for UMS.
The right hand rule is the opposite of the left, how can you learn one without the other? It is a pretty quick thing though, that question is just a little weird.
Reply 34
Windsprite
I don't remember seeing anything about Fleming's Right Hand Rule on the UNIT 5 syllabus ... It seems they just felt like dropping that lil suprise to get our heart's racing.
am I wrong?.


I felt exactly the same. Then I check the specification and realised they don't mention his left hand rule either!

Our textbook only mentions the left hand rule, which wass a source of some confusion for me.
Reply 35
SimonM
I felt exactly the same. Then I check the specification and realised they don't mention his left hand rule either!

Our textbook only mentions the left hand rule, which wass a source of some confusion for me.


Agreed. I only remember the right hand rule from GCSE. Our textbook does not mention anything about it, only the left hand rule.
Our school hardly ever uses text books. Our teachers just teach from what they know, thank god we still have some old skool teachers, the new ones are crap.
SimonM
Motion (at a constant speed) does not need a force.


Yes it does. It needs balanced forces.
Reply 38
Fraser_Integration
Yes it does. It needs balanced forces.


Fine, there must be no resultant force.

If you want to play a game of semantics, what I wrote was correct anyway; if there is no force, there will be no resultant force.
YES! I win.

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