June 2011 G485-Fields, Particles and Frontiers of Physics

Original post by Oh my Ms. Coffey

(8piGp/3)^-0.5 = Age I think.

p = Density
G = Newtons gravitational constant

That's using the formula for the critical density of the universe, not the actual density of it. We can only give the possible fates using that.

Edit: Actually, that gives us the average density, the critical density is the density required for it to be flat..my mistake! :tongue:

(edited 12 years ago)

Reply 761

Oh my Ms. Coffey

Original post by XST

That's using the formula for the critical density of the universe, not the actual density of it. We can only give the possible fates using that.

Not sure how you would answer the question..

Current estimates of the density of the universe are close to the critical density though.

Let's all have a Physics conservation.

Reply 764

Oh my Ms. Coffey

Bed time for me :flutter:

Reply 765

yokabasha

Oh my days I'm such a nerd, I just memorized the whole of the evolution of the universe, the exact times, temperatures and everything.

Oh my days such a nerd...

Reply 766

MRHellen

Could you give me a model answer to the above question please

okay basically the picture wont work but its the one about MRI scanner june 2010 Q5

(edited 12 years ago)

Reply 767

XST

Original post by MRHellen

Could you give me a model answer to the above question please

okay basically the picture wont work but its the one about MRI scanner june 2010 Q5

1. Protons possess a property known as spin
2. In a strong magnetic field, the protons line up and all precess around their axis at the same frequency (Larmor Frequency)
3. A radiofrequency is applied at the Larmor frequency causing the protons to become excited and flip on their axis.
4. Depending on the protons' environment, they will relax at different times and emit an identical radio frequency to the one absorbed.
5. Relaxtion time allows you to know the material in which the proton exists.
6. Small magnets can be placed to create a gradient in the magnetic field.
7. This changes the Larmor frequency at specific points, and a specific radio frequency can be applied to those points.
8. This allows the computer to know in 3D where the proton is in the body and the type of material it is in.

(edited 12 years ago)

Reply 768

Dobson101

How many marks is it?

Reply 769

susan23

3

Original post by Oh my Ms. Coffey

Bed time for me :flutter:

Jesus, I could never sleep this early.

Reply 770

Nirgilis

14

Original post by Oh my Ms. Coffey

Bed time for me :flutter:

Me too me thinks.

A long day that began with C4 and another early start tomorrow for Physics and General Studies... :indiff:

.. May read me book for an hour first though :wink:

Reply 771

MRHellen

Original post by XST

1. Protons possess a property known as spin
2. In a strong magnetic field, the protons line up and all precess around their axis at the same frequency (Larmor Frequency)
3. A radiofrequency is applied at the Larmor frequency causing the protons to become excited and flip on their axis.
4. Depending on the protons' environment, they will relax at different times and emit an identical radio frequency to the one absorbed.
5. Relaxtion time allows you to know the material in which the proton exists.
6. Small magnets can be placed to create a gradient in the magnetic field.
7. This changes the Larmor frequency at specific points, and a specific radio frequency can be applied to those points.
8. This allows the computer to know in 3D where the proton is in the body and the type of material it is in.

Cheers rob

Reply 772

CoffeeStinks

11

Why does fusion produce more energy than fission?

Reply 773

TobeTheHero

15

all nighter for me :smile:

just had 4 hours sleep :smile:

who is with me?

When they ask us to define the Farad or Weber, can you just quote the equation with units? Or do you actually have to learn the definition?

Reply 776

CapsLocke

11

Original post by CoffeeStinks

Why does fusion produce more energy than fission?

fusion reaction binds to nuclei with a small binding energy per nucleon into a nuclei with a very higher binding energy per nucleon.

in a fission reaction the binding energy per nucleon does increase, but not by a lot