June 2011 G485-Fields, Particles and Frontiers of Physics

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

Yes, this links with the X-ray attenuation coefficient where I=Ioe^-ux ( u = mew)

and then the half value thickness x1/2 is the thickness of the material required to reduce the intensity to half its original intensity.

this is where X1/2=-ln2/u ( u= mew) This can be derived by the I=Ioe^-ux equation

where you treat I the intensity as 1 and Io as 2 becuase you want the intenstity to half its original and then divide I/Io = e^-ux then I/Io = 1/2 take natural longs of both sides gives ln2=-ux then rearrange to give X= -ln2/u

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

Hi there, I was wondering can anyone outline the main principles of an MRI scan, in terms of referring to the equipment used such as the gradient coils etc.

Also- there is something that troubles me, why do they setup different larmor frequencies across the patient? Because surely different tissues will have different relaxation times due to their surroundings, so why the use of gradient coils?

I think it is possible for this to come up in the paper - however I most certainly think that the gamma camera and Positive emission tomography scanning, may also come up, it could be 2 out of 3. I guess it would also be very helpful if someone could let us know how radioactive tracers are used to diagnose organs and tissue as well as blood flow in the body.

I was thinking tonight and monday night we have a quiz(keywords).

Tonight we could do Medical imaging and cosmology+ nuclear physics and maybe tomorrow capacitors, electric+magnetic fields.

Hows that sound. I guess we could do it like this:

Just post a keyword question ( I could be the mod in this case for the quiz)
and you post your answers, receive 1 rep for correct answer and nothing otherwise!

Just a way of marking lol!
I dont know if this would work but it could if we have about 5-10 people!


Thank you

Your idea is Ultra Sound.

There are some things that I just don't understand. If someone could kindly give brief explanations to the followings please:

* Fusion and fission
* In a transformer how does the flux linkage change? I understand that the primary coil is connected to an ac supply, but doesn't that mean that the flux linking the secondary coil stays constant? But surely it is changing !?
* Right hand rule or left hand rule? When to use which?

Nothing else is confusing me at the moment.

Thanks.

There are some things that I just don't understand. If someone could kindly give brief explanations to the followings please:
* Fusion and fission
* In a transformer how does the flux linkage change? I understand that the primary coil is connected to an ac supply, but doesn't that mean that the flux linking the secondary coil stays constant? But surely it is changing !?
* Right hand rule or left hand rule? When to use which?
Nothing else is confusing me at the moment.
Thanks.

There are some things that I just don't understand. If someone could kindly give brief explanations to the followings please:

* Fusion and fission
* In a transformer how does the flux linkage change? I understand that the primary coil is connected to an ac supply, but doesn't that mean that the flux linking the secondary coil stays constant? But surely it is changing !?
* Right hand rule or left hand rule? When to use which?

Nothing else is confusing me at the moment.

Thanks.

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

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

Right hand rule or left hand rule.

Let us unravel this problem with an example. Suppose an aircraft is flying east to west, its wings are an electrical conductor cutting across the earth's magnetic flux. In the northen hemisphere, which wingtip will become positively charged?

This seems like a very challenging question at first, but really all we need to do is to find the direction of the force between the wingtips- telling us which direction the positive charge will be flowing. So we use flemings left hand rule for direction of force:

NOTE- northern hemisphere- so magnetic field into the paper, positive charge has a velocity east to west, since the positive charge is between the wings and so we have a current in the direction the plane is moving in, and now you can use flemings left hand rule to workout the direction of the force. So positive moving east to west, direction of magnetic field into the page, and it should give thumb going down the page. We can use the right hand rule to check if this is correct.
Using Right hand rule
magnetic field into the page, thumb east to west, what direction is induced current?

down the page(not into the page, down the page)

I hope this helps!

X

X

I just used RHR you switched the fingers and that's assuming the answer doesn't want the conventional current, do these types of questions always ask for electron flow not conventional current if it doesn't state in the question?

Right hand rule or left hand rule.

Let us unravel this problem with an example. Suppose an aircraft is flying east to west, its wings are an electrical conductor cutting across the earth's magnetic flux. In the northen hemisphere, which wingtip will become positively charged?