last question in section one about particle accelerators (1 Viewer)

[plumo89]

what kind of answer was needed for the last question in section one on particle accelerators?

 

[deyveed]

I think you need to say how the mag field changes its polarity to attract/repel the electron and in doing so, increases its speed.

That's a smart friend's response. Mine was completely off.

 

[Affinity]

your friend's answer is completely off. magnetic fields can't accelerate charges.

F = q v X B (X -> cross product)

W = integral F * dr

but F is perpendicular to v

so work = 0

and no acceleration.

 

[deyveed]

yes!
He's wrong too!
-4 marks for him

 

[Affinity]

You're such a great friend to have

 

[Rahul]

i cant quite remember the question, but i remember writing something like length contraction of the field

 

[freaking_out]

Originally posted by Affinity
You're such a great friend to have

yeah i don't like to have friends like that...

Originally posted by Rahul
i cant quite remember the question, but i remember writing something like length contraction of the field

damn!! i didn't write about relativistic effects.
just used the centipetal force formula to explain it.

 

[toknblackguy]

hmmm...i wrote stuff like it got accelerated between the 'ds' of the accelerator, and as it accelerated, the radius of movement increases, so to maintain the same radius, u increase the strength of the magnetic field. then i said a bit about, as reaching near light velocities, the mass starts dilating, again resulting in larger radius, and magnetic field is again increased. then i wrote down the mass dilation equation
then i wrote
qvb = mv^2
r
and then rewrote it twice to show that magnetic field and radius did something
hehehe

 

[walla]

affinity what do you mean by a magnetic field can't accelerate a charge?

my answer said that there were two increasing quantities, mass and velocity, and i derived that for the centripetal force to be constant (as applied by the magnetic field), the magnetic field must increase in direction proportion to both.

 

[tegs]

I got fully lost. I wrote something about the F=BIlsin equation. Which is wrong I think. I didn't even think about the centripital force equation.
Silly, silly Tegs!!!

 

[Daemontreu]

Originally posted by toknblackguy
hmmm...i wrote stuff like it got accelerated between the 'ds' of the accelerator, and as it accelerated, the radius of movement increases, so to maintain the same radius, u increase the strength of the magnetic field. then i said a bit about, as reaching near light velocities, the mass starts dilating, again resulting in larger radius, and magnetic field is again increased. then i wrote down the mass dilation equation
then i wrote
qvb = mv^2
r
and then rewrote it twice to show that magnetic field and radius did something
hehehe

Well, I hope you're right, because that's what I did!

 

[Constip8edSkunk]

just being pedantically anal the synchrotron dont have dees

Originally posted by walla
affinity what do you mean by a magnetic field can't accelerate a charge?

i might be wrong but i think that the accelerating cavities use high voltage to induce electrical fields to accelerate charges while the magnetic fields from the electromagnets keep the particle in circular orbit.... some thing anyway

 

[Affinity]

yep, magnetic fields CANNOT increase the speed charge particles, no matter how you change the field (yeah I used the word acceleration loosely in my other post), above post gave the general idea, only electric fields can accelerate the charge

 

[ND]

Originally posted by Affinity
your friend's answer is completely off. magnetic fields can't accelerate charges.

F = q v X B (X -> cross product)

W = integral F * dr

but F is perpendicular to v

so work = 0

and no acceleration.

If something undergoes UCM, it's accelerating... (sorry, just being a smartass)

edit: damn i'm too slow...

 

[ESL]

I am not sure but think that question was just another way of asking: "Describe the implications of achieving relativistic speed..." (in relation to time dilation, length contration and mass dilation)... So I'll have to agree wil Rahul on this one.

 

[walla]

ok but still the magnetic fields are, importantly, accelerating the charge around the circular radius (don't care how a synchotron really works i'm talking about the question).
affinity how did you answer the question?

 

[Affinity]

read the other thread.. basically the magnetic field is used to keep the particle in place, it cannot speed it up.

but to keep it travelling in the same radius, the field must increase as a the speed increases, and you have to take in relativistic effects and the gamma factor.

ND: