# June 2011 G485-Fields, Particles and Frontiers of PhysicsWatch

7 years ago
#161
(Original post by TobeTheHero)
you're right lenz's law is all about conservation of energy.

'An induced current is always in such a direction as to oppose the motion or change causing it'
Thats exactly it, it's just a simple induction, and the fact that the induced current is in the *Opposite* direction gives the reason why the equation for magnetic flux linkage is given a negative sign:

0
7 years ago
#162
(Original post by FristyKino)
Agh **** sorry for the neg rep. Didnt mean to press that
I did resat unit 2 aswell. but didnt bother with unit 1 and 3.
Have a mid B in unit 1 and was 2ums points off a b in unit3
Heh, lucky you =P i got a D in every exam so far because i've been so set on Chemistry.. Soooo, im resitting everything now, and all i see when i go to bed is E=MC^2 x_x
0
7 years ago
#163
Do we need to know what quarks and antiquarks make up mesons?
0
7 years ago
#164
(Original post by M_I)
Do we need to know what quarks and antiquarks make up mesons?

I dont think we do, but have a look on the specification ^^^
1
7 years ago
#165
Scratch that.
0
7 years ago
#166
(Original post by Terror)

I dont think we do, but have a look on the specification ^^^
OK...and can you explain how we find the average increase or decrease in binding energy?....Its probably simple, but I don't get it.
0
7 years ago
#167
(Original post by M_I)
Pretty much all of it lol.

Mainly ultrasound and x-ray. I don't get anything about ultrasound and don't get some x-ray equations and questions.....thanks.
here's something on X-ray For you then
X-ray tube: How are x-rays produced in a X-ray Tube and what energy changes take place?

In an X-ray Tube the electrons are emmited from the heated filament (cathode), The electrons are accelerated through a high Potential different in the evacuated X-ray tube towards the Tungston Anode. As the electrons smash into the tungston anode, about 1% of their kinetic energy is converted into X-ray photons. The rest of the 99% of the kinetic engery of the electrons is transffered as heat in the tungston anode. The tungston metal needs to be cooled down due to the bombarding of electrons, so therefore either oil is circulated through the metal or a motor turns the tungston anode to let it cool from one side whilst other parts of the tungston are smashed by electrons. The X-ray photons produced escape through a small window in the led casing in which the X-ray tube is situated. Then the flow of X-ray photons is controlled.

The reason why the X-ray tube is evacuated ( its a vacuum) is because the electrons need a certain amount of engergy to produce X-ray photons as they are decelerated when hitting the tungston anode. So therefore, a vacuum prevents them hitting an gas molecules which would slow them down on the way to the tungston anode.

The is question is worth around 7 to 8 marks but I've given a lot more points for reference.
The process by which electrons are emmited from the cathode in the X-ray tube is called Thermionic emission.
3
7 years ago
#168
Ok with ultra sound, the book just goes off on a mad one and i cant really separate the information needed to anser the syllabus statements, please help.

1) Describe the piezo electric effect

Would this be a big mark question?
0
7 years ago
#169
(Original post by Ralphus J)
Ok with ultra sound, the book just goes off on a mad one and i cant really separate the information needed to anser the syllabus statements, please help.

1) Describe the piezo electric effect

Would this be a big mark question?
No, it came up last time as a 2 marker.
0
7 years ago
#170
(Original post by Oh my Ms. Coffey)
No, it came up last time as a 2 marker.
What do you think will be a big mark question?
0
7 years ago
#171
(Original post by m92singh)
here's something on X-ray For you then
X-ray tube: How are x-rays produced in a X-ray Tube and what energy changes take place?

In an X-ray Tube the electrons are emmited from the heated filament (cathode), The electrons are accelerated through a high Potential different in the evacuated X-ray tube towards the Tungston Anode. As the electrons smash into the tungston anode, about 1% of their kinetic energy is converted into X-ray photons. The rest of the 99% of the kinetic engery of the electrons is transffered as heat in the tungston anode. The tungston metal needs to be cooled down due to the bombarding of electrons, so therefore either oil is circulated through the metal or a motor turns the tungston anode to let it cool from one side whilst other parts of the tungston are smashed by electrons. The X-ray photons produced escape through a small window in the led casing in which the X-ray tube is situated. Then the flow of X-ray photons is controlled.

The reason why the X-ray tube is evacuated ( its a vacuum) is because the electrons need a certain amount of engergy to produce X-ray photons as they are decelerated when hitting the tungston anode. So therefore, a vacuum prevents them hitting an gas molecules which would slow them down on the way to the tungston anode.

The is question is worth around 7 to 8 marks but I've given a lot more points for reference.
The process by which electrons are emmited from the cathode in the X-ray tube is called Thermionic emission.
Thanks

How does increasing the tube voltage give the electrons more kinetic energy? Is there an equation that links the two?
0
7 years ago
#172
(Original post by M_I)
What do you think will be a big mark question?
I think its more likely another topic will come up, but I wouldnt rule Ultrasound out.
0
7 years ago
#173
eurghh i hate G485
medical physics is awful!
been trying to revise electromagnetism...does anyone know the function of a simple ac generator?
0
7 years ago
#174
In X-ray imaging xrays are attenuated by absorption and scattering in three main ways, one is the photoelectric effect.

the cgp book says this:

a photon with around 30keV is absorbed by an electron and ejected from its atom. the gap in the electron shell is filled by another electron, which emits a photon.

are both the photons mentioned x-ray photons????

thanks guys
0
7 years ago
#175
(Original post by Lolly1)
eurghh i hate G485
medical physics is awful!
been trying to revise electromagnetism...does anyone know the function of a simple ac generator?

Isn't it to produce an alternating current (electrical energy) from kinetic energy?
0
7 years ago
#176
Can some one explain Flouroscopy?
0
7 years ago
#177
(Original post by rebmu)
transformers are basically very simple you just have to use the equation vs/vp=ns/np
voltage in the secondary coil divided by the primary coil = numbers of coils in secondary coil/ number of coils in primary coil.
so its basically a ratio thing
so if you're given a question for example that if you needed to step down 230,000 volts to 230v and you had 5000 turns on the secondary coil you would simply
go 230/230,000=1/1000
1/1000= ?/5000 so the awnser is you would need 5 turns in the primary coil.
and for other things you just rearrange the formula accordingly.
and basiclaly step up tranformers have less turns in the secondary coil than the primary coil and for step down transformers as in this example the number of turns in the secondary coil is higher than the number of turns in the primary coil
think the revision guide explains it clearer than me so have a look in cgp
ooh ooh dw i just relzaised what i did wrong i was just being a tard you would have 5 million coils in the primary coil as it should have been rearranged to 1/1000=5000/?
0
7 years ago
#178
Some of these exam questions on electricity are horrible.

Can anyone tell me what they did on page 120 Q3e, and why on Q2cii) It says the rod stays stationary, surely the positive side attracts to the negative plate and vise versa thus turning it.
0
7 years ago
#179
There is SO MUCH PHYSICS!
Dream question:

'Fail to calculate this really difficult capacitor question'

I HATE capacitors more than anything.
0
7 years ago
#180
(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?
The electrons travel through more volts so the eV (electron volts) increases.

An electron volt is a standard unit of energy meaning it can make eV= 1/2 mv^2 so increasing the voltake increases eV and increases KE
1
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