Gauge of wire to use in an induction experiment

[ZapperZ]

The galvanometer has + and - terminals. If current goes in the + terminal, it has a positive deflection.

It is this experiment, but in real life.

https://phet.colorado.edu/sims/html/faradays-law/latest/faradays-law_en.html

Zz.

 

[sophiecentaur]

The galvanometer has + and - terminals. If current goes in the + terminal, it has a positive deflection.

It is this experiment, but in real life.

https://phet.colorado.edu/sims/html/faradays-law/latest/faradays-law_en.html

Zz.

My problem is what direction (from what they know) would the current be, to be 'opposing'? You would need to know the 'other' current, to be sure it's in the other direction. That's why I suggested using a battery. If you don't actually know both the induced current direction and the current it 'would be' opposing then I don't see how they can conclude that Lenz applies - without just believing what they're told.

 

[ZapperZ]

My problem is what direction (from what they know) would the current be, to be 'opposing'? You would need to know the 'other' current, to be sure it's in the other direction. That's why I suggested using a battery. If you don't actually know both the induced current direction and the current it 'would be' opposing then I don't see how they can conclude that Lenz applies - without just believing what they're told.

I don't understand your problem here.

If you look at the simulation, I don't need a battery. I already told you that for the galvanometer, if a current goes into the positive terminal, it will deflect positively. If it goes into the negative terminal, it will deflect negatively. One doesn't need to believe in this. One can easily check it.

Once we know that, and the way the coil is connected, one can see if cw or ccw current IN THE COIL produces a positive or negative deflection.

Then one brings a bar magnet close to one of the opening of the coil. Say it deflects positively. It means that we know that the induced current in the coil is, say, ccw. The direction of the induced current tells you also the direction of the induced magnetic field!

Doing this with several difference scenarios tells you a "pattern" or rules on the nature of the induced current and induced magnetic field.

Zz.

 

[sophiecentaur]

@ZapperZ
You have two options to present /demonstrate Lenz's law to them. You either tell them the field direction in a current carrying coil or they can measure / discover it by using a DC source and the same magnet. Either way, it needs to be known so that it becomes obvious that Lenz's law applies. If you have decided that telling them is enough then that's fair enough. Personally, I would think it more in keeping with a 'learning by doing' approach, not to rely on just telling them.

 

[tech99]

haha that's why I'm here. I wish I could use one of my students as a "lab assistant" sometimes. Trying some of these labs out alone has not been easy.

If you want help with future practicals please ask us here.

 

[ZapperZ]

@ZapperZ
You have two options to present /demonstrate Lenz's law to them. You either tell them the field direction in a current carrying coil or they can measure / discover it by using a DC source and the same magnet. Either way, it needs to be known so that it becomes obvious that Lenz's law applies. If you have decided that telling them is enough then that's fair enough. Personally, I would think it more in keeping with a 'learning by doing' approach, not to rely on just telling them.

Again, I don't understand this.

The students, by this stage, have already studied magnetic fields due to straight wires, loop of currents, and solenoid. So why do I need to tell them the direction of the fields if they know the direction of the induced current?

These are not students I plucked cold off the streets.

Zz.

 

[alan123hk]

I use my own method to solve such problems.

Ampere Loop Law (plus Maxwell's Law) : -
The thumb of the right hand represents the direction of increasing electric field or the direction of current, and the fingers curl in the direction of the magnetic field loops created by it. If the electric field decreases, the direction of the induced magnetic field loop is reversed.

Maxwell-Faraday equation : -
The thumb of the left hand represents the direction of increasing magnetic field, and the finger curl in the direction of the electromotive force created by it. If the magnetic field decreases, the direction of the induced electromotive force is reversed.

I believe that by using the above two rules together with the Lorentz force equation, I can basically figure out all the directions of electromagnetic induction in engineering practice.

 

[sophiecentaur]

These are not students I plucked cold off the streets.

You know that. I didn't, so I was erring on the safe side.
Perhaps the best possible demo of Lenz's Law is to drop a small strong magnet down copper tubes, one with and one without a slot. The braking effect due to Lenz is unbelievable.
I still resent the fact that such magnets were not available when I was a lad. Old bar magnets that I could get hold of were quite pathetic. I could have had a lot of fun.

 

[ZapperZ]

You know that. I didn't, so I was erring on the safe side.
Perhaps the best possible demo of Lenz's Law is to drop a small strong magnet down copper tubes, one with and one without a slot. The braking effect due to Lenz is unbelievable.
I still resent the fact that such magnets were not available when I was a lad. Old bar magnets that I could get hold of were quite pathetic. I could have had a lot of fun.

How long ago since you look at a typical syllabus for an intro general physics course? Magnetic induction is often taught AFTER the students encountered the concepts of magnetic fields and current sources.

Secondly, my setup isn't just about demonstrating this effect. Dropping a magnet through a coil is insufficient to discover the details of Lenz's law. The students need to find out that when they pull the same end of the magnet out, the deflection on the galvanometer is in the opposite direction. And when they use the other end of the magnet, all the induced currents are reversed.

The setup is part of my Studio Physics class where the "lab" is a part of, and integrated with, the actual lesson and lecture.so it isn't just a hand-waving "oh look!" demo.

Zz.

 

[sophiecentaur]

How long ago since you look at a typical syllabus for an intro general physics course? Magnetic induction is often taught AFTER the students encountered the concepts of magnetic fields and current sources.

Is any of that relevant to the thread? It's several years since I actually taught a Physics course.
I am not criticising your teaching methods at all so please do not take offence. The actual OP was not about your particular classes so you can expect a range of reactions along the thread. I have no idea what the "Studio Physics" course comprises, any more than the level of education of your students. I apologise if I raised hackles.

 

[ZapperZ]

Is any of that relevant to the thread?... The actual OP was not about your particular classes so you can expect a range of reactions along the thread.

It isn't, which was why I didn't elaborate much when I posted my first post in response to the OP, because I wanted to show the type of equipment that has worked, and worked very well, in the past. But in Post #28, you then specifically asked about MY setup. You didn't ask anything about the students that these were presented to.

Zz.

 

[sophiecentaur]

It isn't, which was why I didn't elaborate much when I posted my first post in response to the OP, because I wanted to show the type of equipment that has worked, and worked very well, in the past. But in Post #28, you then specifically asked about MY setup. You didn't ask anything about the students that these were presented to.

Zz.

Can't we let this drop and get on with the topic, if there's any more needed?