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Dr Kathy Romer answers your questions about Physics!

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Original post by dnan
Can you just explain the whole of Magnetic Fields in general please? AQA PHYA4


Hello, can you narrow this down a bit?
Original post by Fox Corner
Struggling with a particular theory for your exams? Wondering whether to study Physics at a higher level? Just got a question about the subject in general? :confused:

We're pleased to welcome Dr Kathy Romer to the site for a Q&A session next Tuesday. Kathy is a reader in Astrophysics at Sussex University and a Public Engagement Fellow for the Science and Technology Research Council. She completed her PhD at the University of Edinburgh in The Large Scale Distribution of X-ray Clusters of Galaxies, and is a world expert in the discovery and exploitation of X-Ray clusters of galaxies. :smartass:

Dr Kathy Romer will be answering your questions up until Tuesday 21st June at 6pm.

Post your questions below, and Kathy will try and answer as many as possible. :thumbsup:


Hello Dr Romer,

I have quite a specific question if that's okay. I don't do Physics A-Level myself, but I'm very interested in it! So I was wondering, why does the fact that quarks have colour charge mean that they can only exist inside of other particles? Thank you so much! And this is a great thread! :biggrin:

Best regards,
Edminzodo
Reply 42
Original post by Dr Kathy Romer
Hello Mahrez, I hope you've already stopped revising, since the exam is tomorrow morning. But, as it happens, I've just been discussing this topic with my son - he took a rather extended break from his revision to watch the England game!

If you look at
http://www.bbc.co.uk/schools/gcsebitesize/science/triple_aqa/keeping_things_moving/the_motor_effect/revision/4/

There is a nice video that shows how the splits temporarily stop the current flowing. But the ring keeps turning because it has angular momentum. When current flows again its direction is reversed inside the ring and so the forces remain in the same direction.

Have you seen the unit 2 physics Aqa paper ?
Hello.

Why are the calculus parts of Physics completely ignored in the Physics A/Level curriculum? Do you think it should be reintroduced?



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Original post by Mowerharvey
What exactly is emf, and why does a change in flux induce emf? I've never quite got my head around the concept.


EMF, as I'm sure you know, stands for electro motive force. EMF can be used to describe voltage/potential at a particular instant, but it is no different in concept to the voltage of a household battery (which stays the same for months on end if the battery isn't used).

Imagine a handful of dry spaghetti. Then imagine the same spaghetti after it has been cooked. You can still hold the same number of strands in your fist, but outside of your fist they will spread apart. If a cooked spaghetti strand represents a unit of magnetic flux, then your fist is whatever is squeezing that strand and the other strands together. That "whatever" could be a bar magnet or a solenoid, but it can also be the iron core of the Earth.

Regarding: "why does a change in flux induce emf", now that's the beautiful part. And I'm finding that beauty isn't easy to translate into typed words (sorry). But here goes.... when a charged particle moves it needs to "tell" the Universe. The way charged particles talk to the Universe is through photons. Photons are packets of electromagnetic radiation. You can't have electromagnetic radiation without there being a magnetic field. Hopefully that will convince you that when charges move* a magnetic field is required (i.e. induced).

*actually they need to accelerate - if they have constant velocity, the Universe doesn't care what they do.

The beautiful bit is that the converse also follows: if you change a magnetic field (expressed as "changing flux") then you need an electric field so that information can be transferred. And you can't have an electric field without their being moving charges. If you have moving charges then you need something to move them. That something is the e.m.f.

I hope that helps a bit, and doesn't make the subject even more confusing!
Original post by Sciatic
Hello.

Why are the calculus parts of Physics completely ignored in the Physics A/Level curriculum? Do you think it should be reintroduced?

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Q Why ignored?

A I expect they are ignored because otherwise students not taking Maths A/Level would feel left out/intimidated. But I don't know for sure. The University sector is consulted by exam boards about the content of qualifications, but this isn't something I have personally been involved in.

Q Should it be reintroduced?

I admit that I don't remember back to my A level, so I'm not sure it was part of the syllabus back in the 80's. (So I am not sure if this would be a "reintroduction" or an "introduction").

Either way, I think I'd say "no". It is far more important for students to really understand the concepts of physics pre-University rather than using some calculus that will, no doubt, be at a more trivial (and prescriptive) level than they use in Maths A'level.

For some reason calculus has a status in popular culture as being mega-hard. I'm not sure why that is to be honest....
Original post by MahuduElec
Hi there,

I was wondering what your opinion on A-level physics is (OCR specifically).
Do you or do you not think that the A-level tests study a student's ability in physics/maths, or is it more of just remembering lines for the exam?

Lately I've had trouble finding motivation to revise for my A2 physics exams, especially unit 5 where the majority of it is just remembering standard answers - not the greatest thing I find fun to do.
Do you have any tips on how to sit down and study for topics/ styles of questions for physics that you don't like?

Also, is a career in academia rewarding, both financially and mentally?

Q I was wondering what your opinion on A-level physics is (OCR specifically).Do you or do you not think that the A-level tests study a student's ability in physics/maths, or is it more of just remembering lines for the exam?

A I'll be honest, I don't teach A-level Physics, so I am not qualified to answer. Your teacher would be a better best to ask (especially if they have a Physics degree). However, the A-levels obviously do prepare our incoming students well, because they transition to University level Physics easily.

Q Lately I've had trouble finding motivation to revise for my A2 physics exams, especially unit 5 where the majority of it is just remembering standard answers - not the greatest thing I find fun to do.

A I was a swot at School and V1th form College. By the Easter holiday of my upper sixth I realised I knew everything I needed for the exams and didn't need to revise any more. My friends weren't as prepared as me, so I suddenly had no drinking/dancing buddies at the weekend. So I got a job in a nightclub and saved up for my post A'levels inter-railing adventure.

So... if you aren't motivated because you've already done all the learning you need to do, then think about doing something else (the Euro's are an excellent time waster at the moment I'm finding!).

But if you feel like there is more to learn but you are finding the learning materials too dull, then one thing that I still love doing is trying to explain Physics using unusual analogies. I just did a post relating magnetic flux to pasta. I'd never thought of that before and it made me happy. I did another for the Daily Mail recently relating Dark Energy to a wedding reception.

How about asking your Physics teacher if you can volunteer in a Y10 class, and explain the GCSE material to them using your advanced A'level knowledge?

I admit that I might be the wrong person to ask. Even after all these years, I love Physics. As the old saying goes: "a woman who is bored of physics is bored of life"!

Q: Also, is a career in academia rewarding, both financially and mentally?

A: Yes.
Original post by Mahrez
Have you seen the unit 2 physics Aqa paper ?


From today? No.
Hello everyone, sorry that I've not answered all the questions yet. I will get back to this forum tomorrow evening.

I'm trying to prioritise questions related to exams happening next week, so if that applies to you, please let me know what day you exam is (and the board, unit etc.).

I might not get round to answering the more general questions, e.g. the one about the relationship between physics and medicine, until after the exam questions stop coming in.

Kathy

P.S. please follow @theDESurvey or https://www.facebook.com/darkenergysurvey - our project tries to put out high quality content daily.
Original post by Dr Kathy Romer
Hello. At what level are you studying, and with what exam board? That will help me answer at the right level.


Why do electrons behave the way they do when passed through double slits and behave like a wave, what actually happens?, and could you tell me how the act of measuring with a detector changes the results of this experiment? So strange

are there any other explanations for this besdies schrodinger's probablity ideas? and if this the most plausible expalantion could you explain it to me?
thank you for your time
Reply 50
Hi there,
If an object with mass interacts with the surrounding gravitational field, then why are photons affected by gravity considering that they're massless particles? And since neutrinos have very little mass, why aren't they affected by gravity?
Original post by Nerrad
Hi there,
If an object with mass interacts with the surrounding gravitational field, then why are photons affected by gravity considering that they're massless particles? And since neutrinos have very little mass, why aren't they affected by gravity?


Well, large masses cause disruptions in space-time, curving it around the, for example, planet. Light travels in straight lines, but it will travel in a straight line in this curved space time causing it to appear bent to us (?)

Why do you think neutrinos aren't affected by gravity?

Hopefully Dr Romer will correct/clarify anything I've said :smile:
Reply 52
Original post by Dr Kathy Romer
Hello. At what level are you studying, and with what exam board? That will help me answer at the right level.


i am really interested in both neuroscience and physics, would it be a better route for me to reapply for physics and try to enter neuroscience later, or study neuroscience/biochem and take on physics later

the reason im asking this is because there are suspected links between quantum physics and memory storage/retrieval, and I am very interested in AI
Why can't transformers use DC currents and also why is the induced current in the secondary coil the greatest when the power supply to the primary is being switched of?

Can you explain electromagnetic induction and how emf is induced and then why current is induced?
i'm trying to understand potential dividers for my physics exam next week but i have no idea whether i'm going about it the right way :s-smilie:

if a thermistor or LDR replaces the second resistor (R2) in a potential divider, is it correct to say that when it's cold or dark, the resistance is very high, so there's a high voltage drop. then the voltage across the fixed resistor is nearly 0 as it has a relatively low resistance. so the output voltage would be around the value of the input voltage, meaning a logical 1?

my revision guide explains it in terms of the LDR/thermistor in place of R1 so just wanted to know if that was how it works, if there's anything i missed or got wrong

OCR Gateway GCSE, P6
thanks!
Reply 55
What a levels did you study? What was it about physics that you enjoyed ?
Reply 56
Original post by hezzlington
Well, large masses cause disruptions in space-time, curving it around the, for example, planet. Light travels in straight lines, but it will travel in a straight line in this curved space time causing it to appear bent to us (?)

Why do you think neutrinos aren't affected by gravity?

Hopefully Dr Romer will correct/clarify anything I've said :smile:


Because we learnt in AS physics that thousands of neutrinos are passing through us and the Earth at every moment.
Reply 57
@Dr Kathy Romer Hi, I have an a2 physics exam on monday. I struggle to understand the concepts of Gravitational potential and graviational potential energy.


One of the things I get confused with is the negative sign; my book defines gravitional potential as the work done per unit mass on a small object to move it from infinity to a point in a field.

But shouldnt it be negative when moving a mass from a point to infinity, as you have to work against the field, and positive when moving it from infinity to a point, since the field is pulling it in?

Thank you for your time:smile:
Original post by RBoss
Hi, and thanks for taking our questions!

Just wondering whether you could explain gyroscopic motion in a way which is understandable.. All resources I've found online go a bit too far into theory/complicated explanations.


Hello. I've checked several of the on line materials and I agree they are a bit difficult to follow. I liked this one though https://www.youtube.com/watch?v=zbdrqpXb-fY
Original post by boyyo
@Dr Kathy Romer Hi, I have an a2 physics exam on monday. I struggle to understand the concepts of Gravitational potential and graviational potential energy.


One of the things I get confused with is the negative sign; my book defines gravitional potential as the work done per unit mass on a small object to move it from infinity to a point in a field.

But shouldnt it be negative when moving a mass from a point to infinity, as you have to work against the field, and positive when moving it from infinity to a point, since the field is pulling it in?

Thank you for your time:smile:


Good luck with your exam tomorrow!

I love the fact that you care so much about understanding the sign of your potential.

I hope this helps: Imagine a ball in your hand. Throw it vertically. If you define zero of vertical distance being at your hand, then it starts with zero potential energy (mgh, with h=0). But as it goes higher then potential energy gets larger up to a maximum at the top of its trajectory. Now move your vertical origin to the point where the ball has its maximum potential energy. So that means (mathematically) that potential energy is zero at the top of its trajectory. Likewise that means that when it falls back into your hand, its potential energy is negative.

Generalising this: we define the potential energy of a point mass (i.e. a very small mass) at an infinite distance from a big mass to be zero. That means the potential energy of that point mass at any smaller distance has to be negative.

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