[EricEdwardSelvaraj]

Can anyone confirm the number of significant figures we are supposed to stick to? It usually seems 2 sigfigs but sometimes the mark schemes use 3.

[Oromis263]

(Original post by EricEdwardSelvaraj)
Can anyone confirm the number of significant figures we are supposed to stick to? It usually seems 2 sigfigs but sometimes the mark schemes use 3.

I generally stick to the least numbers of sig.fig. given in the question. If all the numbers given are to two sig fig, I work through carrying all decimals, then round my final answer to 2sf, and I always tell the examiner how many sigfig I've done it to (usually 2sf in brackets etc), just so they (hopefully) see that I'm following the general rule.

[EricEdwardSelvaraj]

(Original post by Oromis263)
I generally stick to the least numbers of sig.fig. given in the question. If all the numbers given are to two sig fig, I work through carrying all decimals, then round my final answer to 2sf, and I always tell the examiner how many sigfig I've done it to (usually 2sf in brackets etc), just so they (hopefully) see that I'm following the general rule.

Thanks that helps, that makes sense. I will do the same.

Also,

What is the mark scheme definition for redshift?

[Oromis263]

(Original post by EricEdwardSelvaraj)
Thanks that helps, that makes sense. I will do the same.

Also,

What is the mark scheme definition for redshift?

The stretching of the wavelength (typically of light when talking astrophysics), towards the radio end of the spectra. That's what I would go for. If it asks about the CMB, I'd mention it is due to the expansion of space in the subsequent years since the big bang, if it asks about distant galaxies, it's a mix of the expansion away from Earth, and then you can talk about how a rotating galaxy shows red shift on one side, and blue shift on the other.

[PhysicsGirl]

(Original post by Quantum_Phantom)
Have you got notes for the other chapters ?

Thanks in advance

Unfortunately, I don't have typed notes for the other chapters, I'm afraid. Sorry!

[Oromis263]

(Original post by PhysicsGirl)
Unfortunately, I don't have typed notes for the other chapters, I'm afraid. Sorry!

The revision day fell through. I only just got home, and I'm trying to force my way through some physics papers. Going to do a mechanics 2 paper now.

[Rotravis]

I actually messed up the Jan 2012 paper when I took it, so it's a great feeling to actually get a good mark on it! Does anyone know how to do the conductance question though? I thought G0 would be the conductance from the question before, but apparently it's not...

[Oromis263]

(Original post by Rotravis)
I actually messed up the Jan 2012 paper when I took it, so it's a great feeling to actually get a good mark on it! Does anyone know how to do the conductance question though? I thought G0 would be the conductance from the question before, but apparently it's not...

I vaguely recall (when I did it as a mock) calculating G0 using the values given in the question, then applying it to the next temperature? Something like that?

[xiyangliu]

(Original post by Rotravis)
I actually messed up the Jan 2012 paper when I took it, so it's a great feeling to actually get a good mark on it! Does anyone know how to do the conductance question though? I thought G0 would be the conductance from the question before, but apparently it's not...

G0 is not the conductance from the question b4 it is the initial conductance. Therefore use your answer from part B find G0 then use the value of G0 find G at 400 k


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[lukas1051]

(Original post by EricEdwardSelvaraj)
Can anyone confirm the number of significant figures we are supposed to stick to? It usually seems 2 sigfigs but sometimes the mark schemes use 3.

Rule of thumb - always go for the least sig figs used in a value in the calculation. Sometimes they allow one over. Bear in mind something like 3.00 x 10^8 is 3 significant figures, whereas 3 x 10^8 is 1 significant figure.

[silvertear]

Hey guys, concerning change of momentum and force:

How does the force actually act on the object the moving object collides and 'exchanges' momentum with?
e.g., is it a two way force? so on the colliding object and the one it hit? I'm struggling with the concept in general

[EricEdwardSelvaraj]

x = 0.18 x sin(2π x 0.38 x 1.5) = -0.08m
This is from legacy June 2010 ms (RF).
I got a different value for this. Can someone please check?

[EricEdwardSelvaraj]

(Original post by silvertear)
Hey guys, concerning change of momentum and force:

How does the force actually act on the object the moving object collides and 'exchanges' momentum with?
e.g., is it a two way force? so on the colliding object and the one it hit? I'm struggling with the concept in general

technically yes, but in practice collisions are inelastic.

[xiyangliu]

It's funny that inertial and torque are not in our syllabus ......


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[silvertear]

Q9. Explain with the aid of a diagram why a moving clock runs slower than a stationary clock.

Light travels further between the mirrors when clock is moving
As speed of light is constant, time taken to travel between mirrors is longer

I understand that the clock will appear to take longer per tick for a stationary person, but why would this mean that less time has passed on the moving clock than if it had not left where the stationary person is?

[PhysicsGirl]

(Original post by silvertear)
Q9. Explain with the aid of a diagram why a moving clock runs slower than a stationary clock.

Light travels further between the mirrors when clock is moving
As speed of light is constant, time taken to travel between mirrors is longer

I understand that the clock will appear to take longer per tick for a stationary person, but why would this mean that less time has passed on the moving clock than if it had not left where the stationary person is?

Okay, so light clocks can be quite confusing without diagrams, but I'll try my best to explain. Imagine you have two horizontal mirrors that are stationary relative to you. Light travels up to the top mirror, which reflects it back down, and you time how long it takes. That's all fine and dandy. In the next scenario, the mirrors are travelling past you. Light travels up from the bottom mirror the same as before, but because the top mirror appears to the observer to move in the time this takes, it is reflected back at an angle and hence takes a longer path than the wholly vertical path in the stationary one. Because speed of light is a constant, and speed = distance/ time, if the distance has lengthened, then time must also be lengthened; therefore, to the observer, the moving clock ticks more slowly.

[heymynameisben]

Can someone give me a hand with 11.d) of Jan 2010. The markscheme (pg 17) says work out A, which I get right. Then put it into E=.5*k*A^2. This gives me the completely different value for E (in the region on 10^-45). Any ideas?

edit- this makes no sense. Just from doing the powers of all the values A squared gives 10^-22 multiplied by k (x10^-23) gives a product of 10^-45. How did they get one to the -20?

[PhysicsGirl]

(Original post by Quantum_Phantom)
Have you got notes for the other chapters ?

Thanks in advance

However, you might be able to find some useful notes here; http://www.gosford-hill.oxon.sch.uk/...rstudents.html

[Ja€k]

(Original post by heymynameisben)
Can someone give me a hand with 11.d) of Jan 2010. The markscheme (pg 17) says work out A, which I get right. Then put it into E=.5*k*A^2. This gives me the completely different value for E (in the region on 10^-45). Any ideas?

edit- this makes no sense. Just from doing the powers of all the values A squared gives 10^-22 multiplied by k (x10^-23) gives a product of 10^-45. How did they get one to the -20?

Isn't that formula for elastic strain energy where K isn't Boltzmann's but the spring constant? If you use K as 30 (from bi) that should work?

[Amy-Rose]

If you're calculating force using F=-GMm/r^2, do you always give the answer as negative? In some markschemes it seems to have changed to positive and doesn't say "accept negative" or anything, but it surely is?