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# OCR Physics B G495 Field and Particle Pictures June 21st 2011 Exam Thread watch

1. I didn't like section c but I don't care! I'm finished!!!
2. (Original post by Kyleidge)
One of the first questions confused me a little
first it asked why the particles path is curved in the magnetic field, then another question asking why it was a spiral...
Aren't they basically the same question?
I just said the force is perpendicular to velocity (etc) for both xD
I said it lost energy as it went round so thats why it spiralled? But I forget to mention radius getting smaller so don't know what I'll get.
3. (Original post by Kyleidge)
One of the first questions confused me a little
first it asked why the particles path is curved in the magnetic field, then another question asking why it was a spiral...
Aren't they basically the same question?
I just said the force is perpendicular to velocity (etc) for both xD
I think, for curved, it was because the magnetic force is perpendicular to the velocity. Then it'd be a spiral because r = mv/bq, and, as the electron collides with the particles of the gas, it thus loses velocity, and so the radius is decreasing and it spirals inwards.
4. Wasn't too bad, I couldnt get the milliare to equal about 2kms though, last night i read that one minute of arc is equal to one degrees. So maybe something went wrong there.

The relativistic factor one went wrong as well, I ended up with a speed faster than light even though my y factor was around 1.7 or something similar. Can't remember even though I've just sat the exam

A few others im not sure about but GL for results everyone.
5. (Original post by arianex)
It was actually! A few slightly "eh" moments like the 4-marker with the beta source and the plates (because I'm not that brill with that bit ), but you gotta admit, that wasn't a ruthless paper at all. ^^

Touch wood for good grades? ^^
I put that the beta particles knock electrons off the ball making it more positive so it moves towards the bottom plate.
6. (Original post by ejw93)
I put that the beta particles knock electrons off the ball making it more positive so it moves towards the bottom plate.
I thought that the beta particles, being negative electrons are attracted to the ball, reducing its positive charge so it is repelled from the top plate with less force?
7. (Original post by Doomfreak777)
Wasn't too bad, I couldnt get the milliare to equal about 2kms though, last night i read that one minute of arc is equal to one degrees. So maybe something went wrong there.

The relativistic factor one went wrong as well, I ended up with a speed faster than light even though my y factor was around 1.7 or something similar. Can't remember even though I've just sat the exam

A few others im not sure about but GL for results everyone.
One minute is one sixtieth of a degree.
8. (Original post by Revolution is my Name)
I think, for curved, it was because the magnetic force is perpendicular to the velocity. Then it'd be a spiral because r = mv/bq, and, as the electron collides with the particles of the gas, it thus loses velocity, and so the radius is decreasing and it spirals inwards.
Oh yeah! Damn, when it said spiral I was thinking circular path, d'oh! nevermind xD
9. (Original post by tiddlytom)
One minute is one sixtieth of a degree.
I used that, and that the arc length = r(theta) when theta is in radians, and got something near 2km, but it did ask you to use the circumference from the previous part, so
10. (Original post by UltraMeh)
This is OCR B, the poster I quoted was talking about a Q that was in OCR A or another exam board. Either way, we do NOT have capacitance in module 5 of OCR B Physics - unless it gets mentioned in Section C or something, which it wasn't.
11. (Original post by Revolution is my Name)
I used that, and that the arc length = r(theta) when theta is in radians, and got something near 2km, but it did ask you to use the circumference from the previous part, so
Circumference/(360x60)
12. (Original post by Doomfreak777)
I thought that the beta particles, being negative electrons are attracted to the ball, reducing its positive charge so it is repelled from the top plate with less force?
Yeah I put electrons are transfered to the ball which cause the ball to become more negatively charged and therefore experience a greater force of attraction to the top plate. This means the ball will move up.
Hope its right.
13. (Original post by Revolution is my Name)
I think, for curved, it was because the magnetic force is perpendicular to the velocity. Then it'd be a spiral because r = mv/bq, and, as the electron collides with the particles of the gas, it thus loses velocity, and so the radius is decreasing and it spirals inwards.
Dang, I mentioned losing energy (and velocity) but didn't talk about colliding with gas particles. Still, it was just a 1-marker... *fingers start grabbing at her wooden desk *
14. Actually really happy with that paper - only question I couldn't answer was a 1 marker "why is this the minimum number of particles" or something at the start and most others I was happy with. Shame this was the good one out of physics/chemistry when I needed a high A in chemistry and only a mid D in this.

God damn spending so long trying to learn why the earth bulges at the equator only for them not to ask though.

For that ball question I wrote that the negatively charged electrons would stick to the positively charged plate, making it less positive and so decreasing the force upwards for the ball causing it to drop lower.

EDIT: By the way anyone notice that the question about pros and cons of the pendulum was answered in the advanced notice article in the same paragraph?
15. (Original post by Rogercbinboy)
Actually really happy with that paper - only question I couldn't answer was a 1 marker "why is this the minimum number of particles" or something at the start and most others I was happy with.
Yeah why is it the minimum number?
16. (Original post by Jke)
Yeah why is it the minimum number?
half of the atoms wouldn't necessarily decay every half life, may be less.
17. (Original post by tiddlytom)
Circumference/(360x60)

Probably won't get the mark, will I?
18. (Original post by ejw93)
half of the atoms wouldn't necessarily decay every half life, may be less.
Doesn't that also mean more than half of the atoms could decay each half life?
So in fact it isn't the minimum number? It's the minimum number on average?
19. (Original post by ejw93)
half of the atoms wouldn't necessarily decay every half life, may be less.
I thought that but it said minimum and I thought maybe less would decay.

Ended up writing that some of them may not be radioactive which i'm pretty certain is bull.
20. (Original post by Rogercbinboy)

EDIT: By the way anyone notice that the question about pros and cons of the pendulum was answered in the advanced notice article in the same paragraph?
Yup. Which made me wonder whether they just wanted you to quote those, or come up with some different ones.

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