OCR Physics A G485 - Frontiers of Physics - 18th June 2015

142 ish

Oh wow, but how did you come up with that, I can't find the ums for a* on the grade boundary website and I know ums doesn't go up linearly

Reply 1081

BrokenS0ulz

3

Original post by Elcor

Part d.ii, it says the lamp has a p.d. of 11.8V and you later have to calculate the current in the secondary circuit; surely this implies a constant e.m.f.?

I think you're right. But since we don't explicitly learn about alternating emf, I think they just want you to take the emf as being constant. They do say at the beginning of d that the emf across the output is 12V, which suggests they're using 12V as the constant emf.

Reply 1082

Raizel

3

Original post by jcwh97

Power = Intensity x Area

Area = 4 x pi x r^2
Intensity = 1400

Substitute and multiply.

Yeah but why is the area 4 x pi x r^2

Reply 1083

BrokenS0ulz

3

Original post by Jim997

Hey guys, can someone give me the definition of :

Activity -
Decay constant -

Activity: the number of particles emitted from a sample per unit time
Decay constant: the probability of decay of a nucleus per unit time.

Reply 1084

randlemcmurphy

11

Original post by Raizel

Yeah but why is the area 4 x pi x r^2

As that is the surface area of a sphere.

Reply 1085

jcwh97

2

Original post by Raizel

Yeah but why is the area 4 x pi x r^2

Its the surface area of the Sun. The sun is a sphere so the formula for the surface area of a sphere is 4 pi r^2

Reply 1086

I Persia I

16

Does anyone have a detailed explanation of this in full? It's from the spec idk how they're all related:

'outline the principles of magnetic resonance, with reference to precession of nuclei, Larmor frequency, resonance and relaxation times'

Reply 1087

L'Evil Fish

OP

18

Original post by leroythelost

Oh wow, but how did you come up with that, I can't find the ums for a* on the grade boundary website and I know ums doesn't go up linearly

A* boundaries are linear

Then it changes as you go up

Reply 1088

leroythelost

10

Guys I don't really understand pulse repetition frequency for ultrasound. I know 1/f is a period but i dont understand how this links to a pulse going there and back. Furthermore, is pulse repetition described as the min or max frequency of the wave because of its call max then that implies a higher frequency messes things up but a higher frequency will make the time for the wave to come back shorter.

Reply 1089

Elcor

14

Original post by BrokenS0ulz

I think you're right. But since we don't explicitly learn about alternating emf, I think they just want you to take the emf as being constant. They do say at the beginning of d that the emf across the output is 12V, which suggests they're using 12V as the constant emf.

I know it says that and it's confusing. I'm not misunderstanding something about induced e.m.f. am I? It should be alternating shouldn't it?

Reply 1090

Raizel

3

Original post by jcwh97

Its the surface area of the Sun. The sun is a sphere so the formula for the surface area of a sphere is 4 pi r^2

Original post by randlemcmurphy

As that is the surface area of a sphere.

ohh I see ty.

Reply 1091

BrokenS0ulz

3

Original post by Elcor

I know it says that and it's confusing. I'm not misunderstanding something about induced e.m.f. am I? It should be alternating shouldn't it?

No I don't think you're misunderstanding anything. It should be alternating because the current is alternating, that's the only way to get an induced emf. They're just simplifying it I suspect :smile:

Reply 1092

BrokenS0ulz

3

Anybody know what to say for compare and contrast decay of radioactive nuclei and decay of charge on a capacitor.

Reply 1093

ForgottenApple

14

Original post by I Persia I

Does anyone have a detailed explanation of this in full? It's from the spec idk how they're all related:

'outline the principles of magnetic resonance, with reference to precession of nuclei, Larmor frequency, resonance and relaxation times'

Literally asked as a past paper question possibly june 10

Reply 1094

Hazza_

1

Original post by SkilledNChilled

What equation? There are two different ones given in the book and it is not said which one to use or to remember it. Also what does it mean by the "car acts as a mirror". How can an image of something move by "2x" if the car moves by "x"? Makes zero sense to me.

I didn't understand the explanation either. That equation they give you is also just an approximation, see my answer on page 12

Reply 1095

Jigardubal

Original post by Raizel

Yeah but why is the area 4 x pi x r^2

Surface area of a sphere that's why

Reply 1096

Jigardubal

Guys can anyone in around 4/5 bullet points list how image intensifiers work please it would be helpful if this included key words

Reply 1097

kate8

2

Original post by actanide

technetium is very transferrable around the body, mixed with glucose and other substances. It can be used to detect if a kidney is healthy. It goes through the kidney the same as water etc, and if the kidney is faulty, itll give off bigger radiation from that area, meaning the kidney doesnt pass liquids well

Whats FDG?

Reply 1098

DoctorDren

2

Original post by jcwh97

file:///C:/Users/user/Downloads/14_Jun%20MS%20(13).pdf

I dont know if this is allowed but here it is

That link cant be accesed but i found it from someone. Thanks anyway

Reply 1099

ETRC

17

Original post by Jigardubal

Guys can anyone in around 4/5 bullet points list how image intensifiers work please it would be helpful if this included key words

-intensifier absorbs x-rays by photographic film
-scintillator is used as an intensifier
-scintillator converts x-ray photon into many photons of visible light
-photons of visible light releases electrons so a lower exposure time to x-rays is needed
-gives a sharper images

OCR Physics A G485 - Frontiers of Physics - 18th June 2015

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