June 2011 G485-Fields, Particles and Frontiers of Physics

Reply 280

Terror

Original post by Pandit Bandit

can anyone explain the nucleon-nucleon spearation graph?

Which nucleon graph..? The stability graph or the binding energy graph?

Reply 281

CoffeeStinks

11

Original post by Pandit Bandit

can anyone explain the nucleon-nucleon spearation graph?

All values <2.4x10^-15 mean that nucleons repel one another. So that they don't compress against each other.

At 2.4x10^-15 they are in equilibrium. Effected by neither the attractive or repulsive force.

All values between 2.4x10^-15<x<5x10^-15 mean that nucleons attract one another. So that they don't fly out of the nucleus.

After 5x10^-15 the strong force has no effect.

This tells us that the strong force has a short range.

Reply 282

jam.wa

8

Original post by Pandit Bandit

can anyone explain the nucleon-nucleon spearation graph?

I assume you mean the strong nuclear attraction graph.

In a nutshell, when the distance between nucleons is...:

- > 2.4 x 10^-15 m = attractive
- < 2.4 x 10^-15 m = repulsive

Reply 283

anshul95

11

Original post by mir3a

How's S3 prep?

Well I have done everything I can - all the past papers, specimen papers, questions in the book. So I am just re doing the ones I only vaguely remember/found hard for extra practice.

Reply 284

Terror

Original post by jam.wa

I assume you mean the strong nuclear attraction graph.

In a nutshell, when the distance between nucleons is...:

- > 2.4 x 10^-15 m = attractive
- < 2.4 x 10^-15 m = repulsive

I think you got the symbols the wrong way round jam.wa, its attractive at less than 2.4 x 10^15 m isnt it?

Reply 285

Gawd

3

Original post by Terror

I think you got the symbols the wrong way round jam.wa, its attractive at less than 2.4 x 10^15 m isnt it?

nope, less than 2.4 x 10^-15 m is repulsive.

(edited 12 years ago)

Reply 286

jam.wa

8

Original post by Terror

I think you got the symbols the wrong way round jam.wa, its attractive at less than 2.4 x 10^15 m isnt it?

No, it's attractive when it's greater than that. When it gets closer and closer, like pressing two balls together, it's going to want to push away.

Reply 287

Terror

Original post by jam.wa

No, it's attractive when it's greater than that. When it gets closer and closer, like pressing two balls together, it's going to want to push away.

Ahhhhh! that makes sense... I guess you learn something every day, just worrying that im still learning things this close to the exam XD

Thanks though =)

Reply 288

Oh my Ms. Coffey

Original post by ChoYunEL

x

Thanks, that's my work for Monday to write up and understand every point.

Reply 289

M_I

Original post by Gawd

I dont have the book, but I think I know what you are on about. I wasn't aware that we had to know much about the quark theory.

I think thats about all we actually have to know.

Reply 290

M_I

Original post by jam.wa

You always draw magnetic field lines going N to S.

Yeah, I thought that was the standard....but they did S to N.

(edited 12 years ago)

Reply 291

m92singh

Original post by M_I

Thanks

How does increasing the tube voltage give the electrons more kinetic energy? Is there an equation that links the two?

They cant ask you how increasing the tube voltage gives the electrons more kinetic energy; in fact its just something you need to remember and you'll get marks for.

Just state:

the intensity of the X-ray beam is the power (energy per second) per unit area passing through a surface (at right angles). There are two ways to increase the intensity of the X-ray Beam:

1). Increase the tube voltage. this gives the electrons more kinetic energy. Higher energy electrons can knock out electron from shells deeper within the tungsten atoms.

2). Increase the current supplied to the filament. This liberates more electrons per second, which then produces more X-ray photons per second.

These are facts you can remember them its all good.

Good luck :smile:

Reply 292

Oh my Ms. Coffey

Original post by m92singh

They cant ask you how increasing the tube voltage gives the electrons more kinetic energy; in fact its just something you need to remember and you'll get marks for.

Just state:

the intensity of the X-ray beam is the power (energy per second) per unit area passing through a surface (at right angles). There are two ways to increase the intensity of the X-ray Beam:

1). Increase the tube voltage. this gives the electrons more kinetic energy. Higher energy electrons can knock out electron from shells deeper within the tungsten atoms.

2). Increase the current supplied to the filament. This liberates more electrons per second, which then produces more X-ray photons per second.

These are facts you can remember them its all good.

Good luck :smile:

Are you sure? More voltage = more work done.

W=Qv so the electrons have done more work if the voltage is increased.

1/2mv^2=Qv.

Reply 293

m92singh

Detection Systems
An intensifier screen may be used to reduce the exposure time for an X-ray image. It consists of
photographic plate between two intensifier screens. Each screen is made from a material such as
Phosphor. Phosphor is a scintillator meaning the energy of a single X-ray photon on it is changed to several
thousands of visible light photons, producing a brighter image ?.
Image intensifiers may be used to produce a brighter real-time image. The expose to X-rays is reduced.
Contrast media includes materials such as iodine and barium. The patient swallows a liquid rich in barium
and the contrast media readily absorbs the X-rays because it has a large attenuation coefficient. Used to
outline the image of soft tissues, such as the intestines.

Reply 294

jam.wa

8

Original post by M_I

Yeah, I thought that was the standard....but they did S to N.

Did they do S to N within a magnet? I think that's what happens on the inside. No idea why.
On the outside it's always N to S

Reply 295

CoffeeStinks

11

Could someone write down bullet points on evidence supporting the big bang model please.

Reply 296

m92singh

Original post by Oh my Ms. Coffey

Are you sure? More voltage = more work done.

W=Qv so the electrons have done more work if the voltage is increased.

1/2mv^2=Qv.

Its in the revision guide for OCR physics A so, i'd go along with it. Hence the fact Workdone= QV as you said.

Increasing the tube voltage gives them more kinetic energy.
Increasing the Current( just more electrons) means there are now more electrons in the same amount of time meaning work done which equals energy transffered is more becuase its more energy (more electrons) for the same amount of time.

Reply 297

Oh my Ms. Coffey

Original post by CoffeeStinks

Could someone write down bullet points on evidence supporting the big bang model please.

Hubble's findings + Microwave background radiation.

Reply 298

m92singh

Original post by CoffeeStinks

Could someone write down bullet points on evidence supporting the big bang model please.

The big bang model assumes space and time evolved from a singularity in an even that took place 12
billion years ago.
- It was infinitesimally small, infinitely dense and very hot. All four forces (gravitational,
electromagnetic, strong nuclear and weak nuclear) were united.
- An expansion of the universe led to its cooling
- At 10^-6s, the temperature of the universe was about 10^14K. The universe consisted of energetic
quarks and leptons.
- At 10^-3s the temperature of the universe was about 10^12 K. The strong nuclear force became
dominant and combined the quarks to form hadrons (including protons and neutrons).
- At 10^7 K fusion reactions between protons produce helium nuclei.
- At 10^4 K, electrons combined with nuclei to form hydrogen and helium atoms.
- Gravitational forces become dominant. Hydrogen and helium clump together to form stars and
eventually clusters of galaxies.
- The temperature of the universe is now 2.7K. It is saturated with EM waves of the microwave
region. On the Earth, this background microwave radiation is isotopic.

(edited 12 years ago)

Reply 299

Oh my Ms. Coffey

Original post by m92singh

Its in the revision guide for OCR physics A so, i'd go along with it. Hence the fact Workdone= QV as you said.

Increasing the tube voltage gives them more kinetic energy.
Increasing the Current( just more electrons) means there are now more electrons in the same amount of time meaning work done which equals energy transffered is more becuase its more energy (more electrons) for the same amount of time.

Likewise if they ask you about increasing the intensity of the tube I was playing around with formula and managed to get this.

I=(Qv/t)/A

June 2011 G485-Fields, Particles and Frontiers of Physics

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