Physics Question Thread

Bibliii

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

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!

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

lucy_

jinx_58

Oh okay! So i do it in that order? And do I just say the following modifications were made, as this will link to my modifications section of the report? Oh and how do you justify the modifications. Do you just say it will increase reliability, and compare this to the oe?

PhytoPlankton

lucy_
Hey lucy_,

@jinx_58 is absolutely right. If I were to recommend an order, this is what I would do:

Briefly explain the original experiment (this can be done at the very start or at the very end of the rationale)
State the independent and dependent variable which should lead onto the below:
You need to discuss the theoretical vs experimental equations. So this is where you discuss how you are going to calculate g from your experimental data and then you need to discuss the equation you are going to use to find the theoretical values for g.
The derivation of the equations (especially for the experimental) needs to be shown, if necessary.
This will then lead to you stating your relationship (like @jinx_58 stated)
And that's basically it.
This should lead to your research question which you may/may not connect to your rationale.

The only issue I find is that when you say you are looking for a value for g, you have to measure two variables and identify a relationship. So it seems you won't be discussing about the relationship/trend as much but rather how you extract/calculate g from that. Is that true or are you expected to discuss the relationship in depth like normal (which would make sense)?

Hope that helps and good luck!

lucy_

PhytoPlankton

I think relationship, as well as extracting g, which I've done but I'm not sure if it's right... I'm not really sure what my teacher wants, because they're new T.T

Once I've done my rationale am I able to share it to you all, just to see if it's okay? I'm wanting to get a 19 this time round, because it is the final! And I'd like to do well in physics (just to make all my tears and sleepless nights were for some purpose and also Asian parents).

jinx_58

lucy_
Feel free anytime to chuck up your rationale, one of us will help out 😊

-jinx_58

lucy_

jinx_58

Thanks!! Now it's time to start writing it and try and not cry from the pain haha

lucy_

Bonsoir bonsoir,

I have just finished writing my rationale. I'm not sure if it's okay to post this on a public forum, as plagiarism detectors, but I would like to get it checked by you smort people! Any ideas on what to do? Tyyy

PhytoPlankton

lucy_
Maybe a shared Google drive link would work?

lucy_

PhytoPlankton

No one would be able to access that, except you guys right? Because I don't want anyone stealing my work 😅

Ohhh, but it says to share the link means to let everyone anywhere have access T.T

lucy_

Bonsoir bonsoir,

Anyway ignoring that for now, and hopefully finding a way to share it privately, but I don't know how to do the uncertainty for 1/sqrt sin theta. It's just against time. I've found the times uncertainty, but I don't understand how to do it for the angle one 1/sqrt sin theta:

Data here! https://drive.google.com/file/d/19m8FXT87ZXdJpq8pzEnf95VSfncP_KaI/view?usp=sharing

PhytoPlankton

lucy_
Hey lucy_,

Yeah, I think you would need our email addresses to share it privately but it seems there's no way of giving my email to your privately either. So, maybe you could make a google drive link, post it really quickly and I can download it and then you can delete/remove the link?

As for your uncertainty question, you do not need to "find" / "calculate" the uncertainty of the independent variable. Since you are not measuring it, there is no uncertainty in its calculations/measurements. There is only uncertainty in the equipment in which you measure the angles (e.g. a protractor). To find that, it's just the smallest increment on the tool which it seems you have already figured out (in the brackets next to the heading Angle). This would apply to the 1/sqrt sin theta as these are not dependent variable values if that makes sense. That 1/sqrt sin theta will stay constant whether or not you do the experiment 1 time or 100 times.

I hope that makes sense.

jinx_58

lucy_
Just let us know when you’re gunna post it and we’ll download it real quick 🙂

-jinx_58

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