Rod's Physics 3/4 Questions Thread

[PB]

With a digram (if you have time), can someone explain what solenoids are? I'm really confused with what we're expected to know

https://www.google.com.au/search?q=solenoid&safe=active&es_sm=122&source=lnms&tbm=isch&sa=X&ei=_tWWU6nwEYi7ygOw3oKgBQ&ved=0CAgQ_AUoAQ#facrc=_&imgdii=_&imgrc=P5wZ2w9o1xf_OM%253A%3B8MjqsG3BMD5GhM%3Bhttp%253A%252F%252F4.bp.blogspot.com%252F-AiqM4GZ5Nug%252FUgS8CKbjIII%252FAAAAAAAACEU%252FcRE9a8zv3Fk%252Fs1600%252F54-solenoid.jpg%3Bhttp%253A%252F%252Fwhat-is-questions.blogspot.com%252F2013%252F08%252Fwhat-is-solenoid.html%3B800%3B369
A solenoid is a coil of wire that loop de loops to form a 'tunnel'. When you run a DC through the solenoid, it creates magnetic field that runs around it and through it. It essentially becomes like a bi polar magnet, for all intents and purposes, when you run a current through it. That is the basic stuff.
But when you start to learn more about solenoids it will become much clearer to you what you need to know. Be patient lol.  Like, they have a  purpose in transformers or generators which is a huge topic later on.

[Rod]

https://www.google.com.au/search?q=solenoid&safe=active&es_sm=122&source=lnms&tbm=isch&sa=X&ei=_tWWU6nwEYi7ygOw3oKgBQ&ved=0CAgQ_AUoAQ#facrc=_&imgdii=_&imgrc=P5wZ2w9o1xf_OM%253A%3B8MjqsG3BMD5GhM%3Bhttp%253A%252F%252F4.bp.blogspot.com%252F-AiqM4GZ5Nug%252FUgS8CKbjIII%252FAAAAAAAACEU%252FcRE9a8zv3Fk%252Fs1600%252F54-solenoid.jpg%3Bhttp%253A%252F%252Fwhat-is-questions.blogspot.com%252F2013%252F08%252Fwhat-is-solenoid.html%3B800%3B369
A solenoid is a coil of wire that loop de loops to form a 'tunnel'. When you run a DC through the solenoid, it creates magnetic field that runs around it and through it. It essentially becomes like a bi polar magnet, for all intents and purposes, when you run a current through it. That is the basic stuff.
But when you start to learn more about solenoids it will become much clearer to you what you need to know. Be patient lol.  Like, they have a  purpose in transformers or generators which is a huge topic later on.

Thanks PB!. We are learning this stuff next week so it should be clearer.
Pretty interesting stuff

[PB]

[Rod]

What does it mean to be perpendicular to a magnetic field of strength??

[lzxnl]

A magnetic field is a vector quantity with a direction

[Rod]

A magnetic field is a vector quantity with a direction

but as in the coils of an electric motor

[lzxnl]

There, they mean one arm of the coil. VCE physics normally considers square coils, so one side must be always perpendicular to the magnetic field direction. Think about it.

[Rod]

There, they mean one arm of the coil. VCE physics normally considers square coils, so one side must be always perpendicular to the magnetic field direction. Think about it.

I see. Thanks Lzxnl

[Rod]

Could someone please explain why when you scrape some pieces of iron, without any magnetic properties, onto a magnet, they temporarily begin to have magnetic properties? I understand the fact pieces of iron that do not magnetize have their particles arranged in a disorganized manner. For iron to magnetize, they apparently must have their particles arranged in this specific way, how does scraping pieces of non-magnetize iron onto iron that does magnetize cause the arrangement of these particles to change?

Also, even after PB's and lxnls great explanations I still don't have a great understanding of solenoids and DC motors. I've asked my teacher for help and he didn't really have the best of explanations Lol. He hasn't formally gone through it, but I still want to know early.
Here's what I know, please edit anything I've said that is wrong and add stuff I've missed or tell me what to read about

Solenoids:
Basically a set of hundreds of circular loops of wire arranged in a tube like way. These hundreds hundreds of circular loops give us an extremely strong magnetic field when current goes through the loops, hence solenoids can be used extensively for purposes in generators or transformers.

DC motors:
The special part of DC motors is the fact it is run by a magnetic field. Parts that make up DC motors are the carbon brushes, commutator, magnet, battery, armature. The forces from the magnetic fields of the magnets make the armature rotate, the turning effect or the rotation of the armature really depends on the forces induced. When one side of the armature has force going down, and the other force going up, we get this maximum turning effect. The more force we get, or current, or coils, the more turning effect, and hence the stronger the motor is.

The commutator changes the direction of the current flow every half cycle to preserve direction of rotation.

The carbon brushes make contact from the commutator to the armature.



thanks

[Rod]

In Oersted's experiment, the compass needle initially points north-south. What would happen if the curren in the wire above the needle ran

a) west-east

b) east-west

I can't even digest the question, don't know what it's talking about. Is it vectors? So if the needle points north, and the current goes west, the needle should move halfway better them? confused

[Rod]

nobooodyss answeringgg my questions grrr haha

I still don't understand magnetic fields around two wires in parallel. I understand that both will attract each other, and that the magnetic field of one wire will affect the other, but don't fully understand.

If one wire, lets say A determines the magnetic field of the other wire, why does the second wire's magnetic field only go into the page whilst the wire A's go out of the page? Really confused, and if this is true, forces act towards each wire, so shouldn't the wires repel instead of attract??

[PB]

Hey Rod,
 I have basically forgotten like everything about magnetism so I am hesitant to help you out. However, I will be back in melbourne after wednesday where I have access to my notes which I can revise and try to help you out

[lzxnl]

Could someone please explain why when you scrape some pieces of iron, without any magnetic properties, onto a magnet, they temporarily begin to have magnetic properties? I understand the fact pieces of iron that do not magnetize have their particles arranged in a disorganized manner. For iron to magnetize, they apparently must have their particles arranged in this specific way, how does scraping pieces of non-magnetize iron onto iron that does magnetize cause the arrangement of these particles to change?

Also, even after PB's and lxnls great explanations I still don't have a great understanding of solenoids and DC motors. I've asked my teacher for help and he didn't really have the best of explanations Lol. He hasn't formally gone through it, but I still want to know early.
Here's what I know, please edit anything I've said that is wrong and add stuff I've missed or tell me what to read about

Solenoids:
Basically a set of hundreds of circular loops of wire arranged in a tube like way. These hundreds hundreds of circular loops give us an extremely strong magnetic field when current goes through the loops, hence solenoids can be used extensively for purposes in generators or transformers.

DC motors:
The special part of DC motors is the fact it is run by a magnetic field. Parts that make up DC motors are the carbon brushes, commutator, magnet, battery, armature. The forces from the magnetic fields of the magnets make the armature rotate, the turning effect or the rotation of the armature really depends on the forces induced. When one side of the armature has force going down, and the other force going up, we get this maximum turning effect. The more force we get, or current, or coils, the more turning effect, and hence the stronger the motor is.

The commutator changes the direction of the current flow every half cycle to preserve direction of rotation.

The carbon brushes make contact from the commutator to the armature.



thanks

Essentially magnetism is due to these things called 'magnetic dipoles'. Think of them like compass needles. When you magnetise something, you apply an external magnetic field which essentially gets these dipoles to line up.
Your commutator specified is only for a DC motor; there are AC motors too.

Solenoids are also useful because the magnetic field inside them is quite uniform.

In Oersted's experiment, the compass needle initially points north-south. What would happen if the curren in the wire above the needle ran

a) west-east

b) east-west

I can't even digest the question, don't know what it's talking about. Is it vectors? So if the needle points north, and the current goes west, the needle should move halfway better them? confused

If the needle points north, the magnetic field is going north. Current going from east to west or west to east will have forces of different directions as given by right hand rules.

nobooodyss answeringgg my questions grrr haha

I still don't understand magnetic fields around two wires in parallel. I understand that both will attract each other, and that the magnetic field of one wire will affect the other, but don't fully understand.

If one wire, lets say A determines the magnetic field of the other wire, why does the second wire's magnetic field only go into the page whilst the wire A's go out of the page? Really confused, and if this is true, forces act towards each wire, so shouldn't the wires repel instead of attract??

The two magnetic fields are separate. Also, objects aren't affected by their own magnetic fields. Try thinking along those lines.

[Rod]

thanks Nliu!

Another question, in transmission wires that carry electricity, I understand how the voltage could decrease and hence how power can be lost as electricity travels from the generator to specific places via transmission wires, but I don't understand why the current will stay the same, and that current can only be decreased if we do specific things (for example using transformers)

Thanks

[Rod]

Oh and just something else,

Has anyone taken a look at the 'exam style questions' in the A+ notes study guide? How close are they to actual VCAA exam questions?

thanks