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

3 years ago
#461
(Original post by a123a)
I agree with this, but do you know if the Doppler shift equation can be used to determine the speed of stars in other galaxies as well as just galaxies?
Should do. Since a galaxy isn't really a unique object with it's own laws, it's just a **** load of stars. So it makes sense that it would work on a specific-star scale, too.
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3 years ago
#462
(Original post by Elcor)
Should do. Since a galaxy isn't really a unique object with it's own laws, it's just a **** load of stars. So it makes sense that it would work on a specific-star scale, too.
Ok thanks for that.
0
3 years ago
#463
In the 2014 paper (q4.c.iv.) you have a capacitor in the standard set up, then it says the power supply is doubled from 12V to 24V and how this affects the temperature change in a bundle of wires.

How do you know to use the W=0.5CV^2 formula and not W=0.5QV

The first formula would say W increases by a factor of 4 (which is correct) whereas the other formula suggests it increases by a factor of 2...

Thanks
0
3 years ago
#464
In the 2014 paper (q4.c.iv.) you have a capacitor in the standard set up, then it says the power supply is doubled from 12V to 24V and how this affects the temperature change in a bundle of wires.

How do you know to use the W=0.5CV^2 formula and not W=0.5QV

The first formula would say W increases by a factor of 4 (which is correct) whereas the other formula suggests it increases by a factor of 2...

Thanks
Oh C is constant so you have to use W=1/2CV^2

Q isnt constant so you cant use the other one
3 years ago
#465
In the 2014 paper (q4.c.iv.) you have a capacitor in the standard set up, then it says the power supply is doubled from 12V to 24V and how this affects the temperature change in a bundle of wires.

How do you know to use the W=0.5CV^2 formula and not W=0.5QV

The first formula would say W increases by a factor of 4 (which is correct) whereas the other formula suggests it increases by a factor of 2...

Thanks
In the first formula the only variable is V as C is constant. In the second formula Q and V are both variables and change as V changes

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0
3 years ago
#466

Oh C is constant so you have to use W=1/2CV^2

Q isnt constant so you cant use the other one
That's it

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0
3 years ago
#467

Oh C is constant so you have to use W=1/2CV^2

Q isnt constant so you cant use the other one
In the first formula the only variable is V as C is constant. In the second formula Q and V are both variables and change as V changes

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Aah okay thankyou
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3 years ago
#468
That's it

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Took me a good couple of minutes of thinking, not sure I could do it in the exam
3 years ago
#469

Took me a good couple of minutes of thinking, not sure I could do it in the exam
Don't worry, capacitor questions look deceivingly simple but actually take a lot thinking. There are so few equations for it so you sit there thinking 'how am I meant to work thus out?!'
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3 years ago
#470
Part 1i on Jan 2013 what direction do electrons flow?
#471
(Original post by Elcor)
Should do. Since a galaxy isn't really a unique object with it's own laws, it's just a **** load of stars. So it makes sense that it would work on a specific-star scale, too.
Works on anything with an associated change in wavelength

You could probably measure the speed of a police car if it has its sirens on and you had something to measure (but c won't be speed of light)

Also works for erythrocytes (RBCs to you and me) and ultrasound, although because you are emitting the wave source and receiving it, you have to multiply by 2
0
3 years ago
#472

Part 1i on Jan 2013 what direction do electrons flow?
Electrons flow anticlockwise negatively charging the plate y. This repels the electrons already present on plate x therefore positively charging it.

0
3 years ago
#473
(Original post by L'Evil Fish)
Works on anything with an associated change in wavelength

You could probably measure the speed of a police car if it has its sirens on and you had something to measure (but c won't be speed of light)

Also works for erythrocytes (RBCs to you and me) and ultrasound, although because you are emitting the wave source and receiving it, you have to multiply by 2
What's c in those cases? The normal wave speed?

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0
#474
(Original post by Elcor)
What's c in those cases? The normal wave speed?

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Yeah in whatever medium
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3 years ago
#475
Do they ever ask you to explain X-Ray in the same way they do MRI/CAT/PET?
3 years ago
#476

Do they ever ask you to explain X-Ray in the same way they do MRI/CAT/PET?
What could you say though? Other than different tissues attenuate x-Rays by different amounts (different word for amounts??)
Ie bone attenuated X-rays by a large amount. Soft tissues attenuate x-Rays minimally. Hence x-Rays pass through soft tissues more than bones.

Just off the top of my head.

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3 years ago
#477
What is the hardest
G484 paper-

G485 paper-

Out of all the years in peoples opinion
3 years ago
#478

What is the hardest
G484 paper-

G485 paper-

Out of all the years in peoples opinion
I think the June 2014s for both of them. The others don't seem as hard as them.
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3 years ago
#479
(Original post by sagar448)
I think the June 2014s for both of them. The others don't seem as hard as them.
Dam that isnt good for us then!! 2015 will be even harder
3 years ago
#480

Dam that isnt good for us then!! 2015 will be even harder
Yeah I know :C. I'm very scared I just hope I don't mess up.

EDIT: There still maybe a chance to find out if they are going to be hard or not. I'm retaking the G482 which is on the Thursday of this week, and if that one goes well, I'm guessing the others will be fine too.
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