June 2011 G485-Fields, Particles and Frontiers of Physics

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Is the quark model for Beta - decay:
udd to uud ?

As some confusion as text book saying different to mark scheme of June 2010

Yes, that is correct.
Think of it this way. In Beta- decay, the proton number goes up, so this tells you that a neutron is converted into a proton. A neutron is UDD, so this conversion is UDD-->UUD.
In Beta+ decay, the proton number goes down, as a proton is converted into a neutron. Since a proton is UUD, this conversion is UUD-->UDD.

Reply 561

MarieLyon

Original post by sulexk

This is actually EMF against time I believe, since in the initial position we have maximum flux linkage

oops sorry I contridicted myself from earlier. I thought we were still on about from the vertical postion (not cutting any lines)

Reply 562

yokabasha

Original post by Oh my Ms. Coffey

Original post by MarieLyon

thats magnetic flux against time.

Nh its voltage against time aint it, cause the area of the coil is perpendicular to the field, so flux is max, therefore voltage is zero, cause the rate of change of flux linkage is = voltage

Reply 563

Captain Hob

I'm a little confused by the mark scheme for the February 11 paper, question 6(b).

The present mass of the Sun is 2.0x10^30 kg. The Sun emits radiation at a rate of 3.8x10^26 J/s. Calculate the time in years for the mass of the Sun to decrease by one millionth of its present mass.

In the mark scheme, the change in mass is taken to be 2.0x10^24 kg. Surely if the mass were to decrease by one millionth, it the change in mass would be 2.0x10^6 kg? :confused:

In other news, I hate OCR.

Reply 564

MarieLyon

Original post by yokabasha

Nh its voltage against time aint it, cause the area of the coil is perpendicular to the field, so flux is max, therefore voltage is zero, cause the rate of change of flux linkage is = voltage

I know, I know - I mis-read it.

why morning!?

Original post by Captain Hob

In other news, I hate OCR.

see, i thought that. i tried to times by 1/million and got a stupid number.

Reply 567

sulexk

Original post by Captain Hob

In other news, I hate OCR.

Actually I see what you mean, if it said "to one millionth of its present mass" then that would be correct, but saying "by one millionth" indicates subtracting a millionth from its initially mass, which would be almost insignificant.

Reply 568

MarieLyon

Original post by sulexk

it does, i did both ways its pretty much negliable.

Reply 569

susan23

ok can someone explain this to me....

when you have a coil rotating in a magnetic field and you produce a voltgae against time graph

the MAximuM magnetic flux is when the voltage is zero? because the maximum cut is when the coil is just a bit over perpendicular and just a bit below perpendicular so the difference is large? does that make sense?

sorry for the **** picture, i had no idea how to explain it otherwise...

(edited 12 years ago)

Reply 570

Lengalicious

Original post by sulexk

THE BIG QUESTION ON ELECTROMAGNETIC INDUCTION!

This is presumed to be a very challenging question- if you can do it, feel free to explain it to us!

3ai) Magnetic flux is flux density x the area through which it passes BA
aii) flux = BA where A = x^2 therefore flux = Bx^2, linkage is number of coils therefore flux linkage = NBx^2

bi) emf = rate of change in flux linkage
- therefore flux linkage over 0.2 s is 1250x0.032x(0.02)^2/0.2 = 0.08 v which translates to 80 mV

(edited 12 years ago)

Reply 571

balloon92

Also how would you calculate the force at the midpoint between two charges?

Reply 572

Captain Hob

Original post by MarieLyon

see, i thought that. i tried to times by 1/million and got a stupid number.

Original post by sulexk

Glad it's not just me then. Hopefully they're not that vague tomorrow.

Reply 573

susan23

Original post by balloon92

Also how would you calculate the force at the midpoint between two charges?

its usually zero i think.

Reply 574

Lengalicious

Original post by susan23

its usually zero i think.

wrong

Reply 575

susan23

Original post by Lengalicious

wrong

well it depends if its a neutral point or not. if not then its not zero. depends on the charges and what the fields are lke

Reply 576

Captain Hob

Original post by balloon92

Also how would you calculate the force at the midpoint between two charges?

Coulomb's law, using the product of both charges and the total distance between them.

Reply 577

Lengalicious

Original post by susan23

well it depends if its a neutral point or not. if not then its not zero. depends on the charges and what the fields are lke

think of how ridiculous that sounds if its a neutral point then its not between two charges.... the field is weakest at the centre between 2 charges but if they are interacting there is always a field strength as the definition of charge is 'not neutral'

Reply 578

muffingg

A 20 uF capacitor is charged up to 200V and then disconnected from the supply. It is then connected across a 5.0 uF capacitor. Calculate the energy dissipated when they are connected together.

(u = microFarad 10^-6)

Anyone please?

(edited 12 years ago)

Reply 579

Pheylan

Original post by sulexk