things to clear up (1 Viewer)

[Steven12]

alrite, i was going through my notes and i need to confirm this.

Messiner effect is the induction of eddy currents on a superconductor by a falling magnet., the magnetic field of eddy current is so strong that it is able to completely repel the external magnetic field (lenzs law), causing magnet to levitate above the superconductor? right?

okay

I dont know about you but i always have trouble finding the direction of the induced current in multiple choice. you are give a picture of a ac or dc generator, are are told which way the the armature spins, and the direction of external magnetic field(north pole to south pole).

Now what i want to know is that how you apply the right hand rule here. Does my thumb point against the direction of the rotation(by lenz;s law). and my other finger in the direction of the external magnetic field and thus work out which way the current runs?(or should it also work the other way around?)

now third.

what is a majority and a minority carrier( to do with semiconductors?)
i know one of them is a free electron and other a free postive hole


thank you very much and i hope you have a good exam.

 

[lil_kimmy]

i dont think the meisner effect is about eddy currents. When a superconductor is in its superconducting state, current flows in the superconductor to produce a magnetic field that cancels the magnetic field inside the supercondctor. This expulsion of field is the Meisner effect. If a small magnet is brought near it, repelling poles will be produced.. that levitates it.

and for your right hand rule one.. the thumb points in direction of conventional current! so if they give u the way electrosn flow.. u point it in the opposite direction.. and fingers in the external magnetic field and ur palm should be the way the armature spins.

and i have no idea what majority and minority carriers are! i've only heard of holes as positive carriers and electrons as negative..

 

[wind]

To find the direction of the induced current you use the modified right-hand palm rule.

Your thumb points in the direction of movement, fingers in the direction of the magnetic field and your palm represents the direction a positive charge will move.

 

[helper]

alrite, i was going through my notes and i need to confirm this.

Messiner effect is the induction of eddy currents on a superconductor by a falling magnet., the magnetic field of eddy current is so strong that it is able to completely repel the external magnetic field (lenzs law), causing magnet to levitate above the superconductor? right?

What you said is true but insure you talk about the balance magnetic and gravitational forces.
The Meissner effect is a bit more than that. The superconductor will actively exclude the magnetic field even if the magnet is stationary.

okay

I dont know about you but i always have trouble finding the direction of the induced current in multiple choice. you are give a picture of a ac or dc generator, are are told which way the the armature spins, and the direction of external magnetic field(north pole to south pole).

Now what i want to know is that how you apply the right hand rule here. Does my thumb point against the direction of the rotation(by lenz;s law). and my other finger in the direction of the external magnetic field and thus work out which way the current runs?(or should it also work the other way around?)

What you have said is one way of doing it. The only thing to add is the palm will be pointing to the positive pole if there is no external path for the current to flow.

now third.

what is a majority and a minority carrier( to do with semiconductors?)
i know one of them is a free electron and other a free postive hole


thank you very much and i hope you have a good exam.

Not sure what your talking about here. It sounds like an extra term that you don't need to know. I would say the majority carrier is the free electrons and minor carrier is the positive hole due to the relative numbers of each.

 

[wind]

P-type semiconductors:

Majority carriers: holes
Minority carriers: electrons

N-type semiconductors:

Majority carriers: electrons
Minority carriers: holes

 

[sub]

so majority minority is based on the number of each present in the doped semiconductor?

 

[Steven12]

What you have said is one way of doing it. The only thing to add is the palm will be pointing to the positive pole if there is no external path for the current to flow.

external path, by that do you mean a complete circuit? so if there is no external path(like a metal rod), thing induced current goes toward postive terminal?

 

[wind]

Yup!

It's basically which one of the two types determining what becomes the majority/minority. Pretty simple

 

[sub]

hey apparently doping doesn't affect the charge but affects the electrical conductivity...do we need to talk about this?

 

[helper]

external path, by that do you mean a complete circuit? so if there is no external path(like a metal rod), thing induced current goes toward postive terminal?

If there is no external circuit you do not have a current flowing rather a seperation of charges. On end of the conductor becomes positive and the other negative.

 

[helper]

hey apparently doping doesn't affect the charge but affects the electrical conductivity...do we need to talk about this?

MAke sure you don't talk about a n-type conductor as being a negative conductor or p-type as a positive conductor.
Or anyway refer to a semi-conductor having a charge.

 

[wind]

hey apparently doping doesn't affect the charge but affects the electrical conductivity...do we need to talk about this?

You need to describe how doping changes the electrical properties of a semiconductor, relating it to the number of electrons and holes.

When conduction happens in a pure semiconductor, the material is called an intrinsic semiconductor.

When conduction occurs in a doped semiconductor, the material is called an extrinsic semiconductor.

 

[sub]

yeah i know about intrinsic and extrinisic, i get hhow the electrical properties change and all, but do we have to mention that there is no electrical charge on the semiconductor due to the doping, or will they assume that's the case.

 

[helper]

They will assume it if you describe correctly how they are doped.

A lot of people in past HSCs have described how a conductor works by saying things like an extra electron making them a negative conductor or a missing electron.