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OCR Physics B G495 Field and Particle Pictures June 21st 2011 Exam Thread

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You seem to undersand the basics, i wwouldnt worry about the harder details too much, the answer is usually ----- induces ---- which causes -----. There are more marks involved in the calculations. Make sure you can draw flux lines, look over the hand rules, and practice some emf flux flu density calculations etc.

Yeah I'm fine with all that, just looks like this might be a big part as it wasn't in the previous two papers. Any other suggestions what might come up or that i should make sure i know?

Reply 461

Geekchic17

Original post by Anthz

Anyone care to clarify electromagnetic machines?
Transformer: AC -> Alternative Flux -> Eddy currents due to AF causing current in the core -> Current produced in secondary
Generator: Movement -> Current
Motor: Current -> Movement
Last two confuse me a bit, any help in how its formed.

I wrote up generators and motors (on two different replies) on previous page (21)

as for transformers:

eddy currents are produced in the core, not the coil, hence not useful
eddy currents transfer magnetic energy into heat energy, wasting energy, hence lowering the efficiency of the transformer

6 steps to transformer
1. Input AC into primary coil
2. This makes a changing magnetic field in the core
3. Flux linkage is concentrated by the iron core in the secondary coil
4. The flux linked with the secondary coil changes
5. This induces an emf in the coil, (emf = d(Nphi)/dt
6. This then creates an alternating current in the secondary coil, providing that the secondary coil circuit is complete

So almost lol

Reply 462

Sereni

Original post by Summerdays

That makes sense. But why is it the equator that is used to keep the earth spinning?

Because the earth spins in a circle, it spins around the axis, the equator is the bit of the earth that is around the axis it spins round, if for example the earth spun around a different axis like around an axis joining england and australie then the earth would bulge in different places.

Think about how the earth spins, the north pole doesnt actually move much, whereas the equator is the bit that spins and so that is the bit where gravity is used to keep it spinning.

Reply 463

Swindan

Are energy levels of a particle just how many De Broglie wavelengths the particle completes in one orbit of it's nucleus? Or is this completely wrong?

Reply 464

Summerdays

Original post by Sereni

Thank you. This makes sense now :smile:

Reply 465

Sereni

Original post by Anthz

Yeah I'm fine with all that, just looks like this might be a big part as it wasn't in the previous two papers. Any other suggestions what might come up or that i should make sure i know?

Particle accelerators seem popular, and radiation. Tbh its 2 hours, they will probs cover most of the specification

Reply 466

Summerdays

Original post by Swindan

Are energy levels of a particle just how many De Broglie wavelengths the particle completes in one orbit of it's nucleus? Or is this completely wrong?

This is correct :smile:

Reply 467

Sereni

Original post by Swindan

Are energy levels of a particle just how many De Broglie wavelengths the particle completes in one orbit of it's nucleus? Or is this completely wrong?

Energy levels are all about the energies the electrons may have to remain stable, when bound to the atom they have to have these levels, im not aware that we have to know how they come about as i was under the impression it involves a quite complex quantum explaination. In past papers its all been about what happens when electrons jump up/down energy levels and using stuff like E=hf

Reply 468

Geekchic17

Original post by Swindan

Are energy levels of a particle just how many De Broglie wavelengths the particle completes in one orbit of it's nucleus? Or is this completely wrong?

Pretty much I think
these are useful:

E = hf = hc/lambda

lambda = h/p

You'll probably be asked on evidence for these energy levels, so mentioning Line Spectra (Emission and Absorption Spectra)
where:
Absorption shows the wavelengths absorbed by the electrons to excite them to a higher energy level (Colourful spectra) and
Emission shows the wavelengths of photons emitted when the electron falls down energy level(s)
Energy carried by each photon is the difference in energy between the two levels.

The wave model helps to understand energy levels mainly

Reply 469

JoeCarr

I think it is finally time to say it....

I am ready. :dumbells:

Reply 470

Geekchic17

Why are protons and antiprotons always created in pairs?
Is it just that for every matter there is antimatter, or is there something more complicated than that that I'm missing out on here?

Reply 471

Summerdays

I GET IT NOW:

The eart spins around its own axis, and the equator lies in this axis, this means that the equator must be providing the force to keep the earth rotating. This means that via a centrifugal force, the pressure difference across the element is less (by causing the element to reduce its volume, PV = constant.) A reduction in the force due to pressure difference causes the gravitational force on the element in the equatorial plane to out-balance this force due to the pressure difference. This resultant force provides the centripetal force for circular motion. Because the volume of the elements in the equatorial plane increases, the equator bulges outward. But because no resultant force is needed from the elements that lie in the poles, and because the volume of the earth must be maintained, the poles flatten.

(edited 12 years ago)

Reply 472

Summerdays

Original post by Geekchic17

Why are protons and antiprotons always created in pairs?
Is it just that for every matter there is antimatter, or is there something more complicated than that that I'm missing out on here?

To conserve charge, momentum and Baryon number. :smile:

(edited 12 years ago)

Reply 473

Harry.C

Suscribed for tomorrow. Good luck y'all.

Reply 474

Alex.Stevens

Original post by Geekchic17

Why are protons and antiprotons always created in pairs?
Is it just that for every matter there is antimatter, or is there something more complicated than that that I'm missing out on here?

Also you have to create an equal amount of matter and antimatter.

Reply 475

jimmeh

Original post by JoeCarr

I think it is finally time to say it....

I am ready. :dumbells:

I think I'll join you on that. Apart from reading the pre-release stuff properly...But I need something to do on the bus in tomorrow...

Reply 476

Summerdays

Original post by Alex.Stevens

Also you have to create an equal amount of matter and antimatter.

This isn't necessary. Remember that energy and mass (matter) are interchangeable.

Reply 477

Mikkels88

Original post by JoeCarr

agreed man, we may have to put up with ****ty brum brum jokes in primary school, but at the end of the day it's a great surname.

want to hear something that takes it to the next level though? My mum's maiden name was..............Driver. No.word.of.a.lie. Imagine how cheesy a chat up line it would sound if my dad asked for her name, and then said when she asked for his, 'I can be the car to your driver' or w.e.... :colondollar: