Physics Question Thread

Bibliii

Hiii,

Could anyone please explain the right hand rule for electromagnetism. Also what does conventional current mean (is it the positive to negative or something like that is flippity flopped?)

Thank youu

God

Bibliii

Hi Bibliii,

Conventional current is what we use to describe most circuits. It is the flow of charge (specifically positive charge).

In chemistry, you view current as the flow of electrons. But because electrons are negatively charged, and old science people were stupid and thought they were positive, it is in the opposite direction.

All u need to know is that conventional current flows from positive + to negative -!

Where as the electrons flow from negative to positive.

2) In terms of the ‘right hand rule’ there are two main ones.

Magnetic Force on a moving charged particle.
Thumb in direction of current (direction the + charge is moving), fingers in direction of magnetic field, and ur palm shows the direction of the force.

If it’s an electron, which is negative, u point ur thumb in the opposite direction to the electrons movement.

Magnetic Field from a wire.
Thumb in direction of current. Curl fingers like a fist. Looking at it from the pinky end shows which way the magnetic field runs (clockwise/anticlockwise)

There are two more, one for Lenz’s law: which is finding which direction the current must flow when a coil of wire is moved in a magnetic field. And one for finding the north/South Pole of a coil of wire (solenoid). But u can also use the magnetic field one instead, it just hurts ur head a bit more.

Hope this helps,
-G

Bibliii

God ahh thank you so much, that was there helpful!!

Bibliii

Hiii, I finally got drive to work so now I can share images.

These are my physics homework questions, that I cannot do for the life of me (because content goes too fast, and my teacher loves to single me out because im the slowest learner in the class and because she is completely racist). I attempted drawing on the worksheet (question 1) it has diagrams and isn't one of the Pearson's questions. I can't answer any though, because I am so bad at physics right now. And my tutor didn't give me any notice before telling me that she couldn't tutor any more (though she has a new job, so good for her ig). But yeah, I am quite literally freaking out and there are so many questions, not too mention whole entire chapters to read. So yeah, life's been a bit hectic.

If any of you could help by even answering just one question, you would be a lifesaver. Thanks, 🙂

jinx_58

Bibliii
For the first image, I had trouble with 5) aswell in yr 12 haha, so here’s @PhytoPlankton answer: https://imgur.io/a/asiRhTD

These two links should help with the rest of that first image:
https://ibb.co/WpRxJJZ
https://ibb.co/tQHqm5j

-jinx_58

PhytoPlankton

Bibliii
Thanks @jinx_58 for your reply!

Hey Biblii,
Here is the link to the solutions for the rest of your questions in the last four images (I've combined the 8.1&8.2 Review questions and I combined the physics WS p1&2): https://imgur.com/a/JSg6pso.

Sorry for my messy handwriting and image drawings - I was doing this in a hurry 😅. Nevertheless, hope this helps and as always, feel free to ask more questions.

EDIT: now that I quickly check over my workings, I notice there are a few spelling and grammar issues. Just try and ignore them - sorry!

Bibliii

PhytoPlankton and jinx_58

Hii, first of all, thank you for responding to this faster than my teacher has ever (I panicked and sent her an email saying I was sorry if I hadn't completed the homework). I just wanted to clarify a few things with the questions.

For question 3 on 8.1 review, the answer you wrote was the "north pole of the magnet will point as geographic north which is the magnetic south pole". Does that mean that the magnet is facing magnetic south pole (the north part at least)? Sorry, I'm just a bit confused. Also with the calculations for all the answers that involved actual maths, it's just subbing in information into the formula and then just using ratios sometimes?

For 8.2 review wouldn't question 5 and 6's answers be switched because A is closer to LHS which is west (for question 5), or is my brain just disintegrating.

For the worksheet, (d) Aluminium metal is not affected by a magnet. Can an aluminium wire create a magnetic field? The answer would be no, wouldn't it. Because magnets only work in magnetic fields, right?

Thank you both so much for answering those questions, you all will now be given the "saved my butt award".

P.S. PhytoPlankton your handwriting is literally so neat, so umm not sure what you're talking about haha. Nevertheless thank youuu to both of you guys!!

jinx_58

Bibliii
For question 3 on the 8.1 Review, there’s this concept that the geographic North Pole - where Santa supposedly lives - is scientifically a South Pole. This is because the geographic North Pole attracts other magnetic North Poles.

I hope this diagram helps: https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSqTPohiHrQQezAvOsUd-BBOOAuaK1PDzBIOw&usqp=CAU

Idk if that makes sense but feel free to ask more questions.

Also with the “magnets only work in magnet fields” thing, that not how it works. A magnet creates its own magnetic field. Every single one. So, because the Earth is a giant bar magnet, it creates it own magnetic field.

However, if aluminium wire has a current flowing through it, a magnetic field is present. Any wire with an electric current creates a magnetic field. Check out the syllabus and the syllabus glossary, it really helps to see what QCAA actually want lol.

-jinx_58

PhytoPlankton

Bibliii
Hey Bibliii,

All good - we're all happy to help!

For the 8.2 review questions 5 and 6, it is a bit tricky and I just realised I didn't really explain it that well. So the main thing you need to do is draw the magnetic field lines on both magnets. As soon as you do this, you will notice that since both are north poles, the lines of each one will come towards each other (--> <--). So if we take a look at point A, would the LHS or RHS magnetic field line be stronger? It would definitely be the LHS magnet because it is closer and the RHS magnet would have a much weaker magnetic field line. So, now you need to take both of those magnetic field lines as vectors and find the vector sum so like this: ------> + <--- = --->. And that final arrow is pointing towards East. Does that make sense?

Hope that clears it up and as always, let us know if you have any other questions.

Bibliii

PhytoPlankton yes I do get it now, haha thank you so much for clarifying!! Sorry I didn't reply sooner to you both, the internet in my area sucks rn

Bibliii

Hiii everyone,

I was just wondering if I coul get some help with these physics questions? Also I do have an answer for question 5, which is that it has to be sin and not cos because sin has a minimum value of 0, whereas cos does not (dunno if that's right or makes sense but yeah).

https://drive.google.com/file/d/11yPRllFWncm8MNNbQhlfoXY6ZdrbrbBy/view?usp=sharing

https://drive.google.com/file/d/18FUdb-NU0mGWl0SIxxCB2e_kS4jEGgB4/view?usp=sharing

https://drive.google.com/file/d/1ABEEPwn5TjH3Z5udojgMWyEFrjzqAyQg/view?usp=sharing

Thanks!!

PhytoPlankton

Bibliii

Sorry Bibliii, I completely missed this! Would you still like help with these questions?

PhytoPlankton

Bibliii
Hey Bibliii,

Here are my answers to the theory questions in your first image. I skipped number 1 as I believe Lorentz force is a topic that is not in the syllabus and thus, you do not need to know (correct me if I'm wrong). However, if you like, I can take a look at the questions anyways.

If you take a look at either the centripetal force equation (F=mv²/r) or the centripetal acceleration (a=v²/r) equation, you will notice that if you double the velocity (i.e. 2v) then due to the square, it will become 4v². This means that the radius will increase by 4 times the original if you double the velocity.
Sin(theta) is used as this gives the perpendicular component (y-axis) whereas cos(theta) would give the parallel component (x-axis). The component that is needed to represent the force relative to the magnetic field is the perpendicular component which is why sin(theta) is used.
a) If the particle is positively charged, the direction of the force would be down. So, in this case, it would take path C.
b) C (answered above as well)
c) The kinetic energy should remain constant as the circular trajectory has a displacement of 0 and thus, there is no work done. No work done means no change in kinetic energy (according to the work-energy theorem).
d) Negatively-charged particles would go up (path A)
e) A neutral particle would travel in a straight line (path B) as magnetic fields only affect charged particles.

Hope this helps and answers your questions and let me know if you have any other issues!

Bibliii

PhytoPlankton

No problems!! That would still be great thanks, I can do the questions with calculations now, I just need some help with the first few which are more theory based!

lucy

Bonjour or bonsoir,

I've just started my physics student experiment and was wondering if anyone could perhaps help me! PhytoPlankton (I think) helped me find this, so thank you to them!

jinx_58

lucy
Hey Lucy! Any specific questions?

-jinx_58

lucy_

jinx_58

Umm maybe how to write a good rationale, ofc I know the basics, like put all the theory and stuff, but I'm really not good at explaining that theory. I'd really like to do well as this is my last year, and I hope to get into med so any help or checking of work would be appreciated!

lucy_

lucy_ jinx_58

Oh if you need more info the practical is rolling a mass down different angles of an inclined plane and then finding the value for g. Measuring t and angle (I'm pre sure)¡

PhytoPlankton

lucy_
Hey lucy_,

@jinx_58, I don't want to steal your thunder here 😆 but just wanted to let you know, I did the exact experiment in Grade 11 so I would be happy to help and add to anything @jinx_58 has to offer.

lucy_

PhytoPlankton

Bonsoir bonsoir,

That would be amazing, I'll take any and all help!! My rationale is due Tuesday so ima take up as much help as possible!

jinx_58

lucy_
One main thing to talk about in the rationale is the independent and dependent variables, and how they affect each other. Then you use the equation, and explain the equation itself. For example, does g decrease or increase as the angle increases? What sort of relationship is it e.g. inverse proportional, directly proportional, exponentially increasing etc. How is this shown through the equation. Remember to talk about modifications and how exactly they improve the original experiment. @PhytoPlankton I am more than happy if you shoot tips and everything, I don’t see it as stealing my thunder haha

I also highly suggest thoroughly understanding the marking criteria

Hope this helps,
-jinx_58

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