OCR ADVANCING PHYSICS B G494 EXAM MONDAY 18th June

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.

Reply 81

Oromis263

2

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. :smile:

Reply 82

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. :smile:

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

Also,

What is the mark scheme definition for redshift?

Reply 83

Oromis263

2

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. :smile:

Reply 84

PhysicsGirl

OP

7

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!

Reply 85

Oromis263

2

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. :smile:

Reply 86

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...

Reply 87

Oromis263

2

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?

Reply 88

xiyangliu

2

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

This was posted from The Student Room's iPhone/iPad App

Reply 89

lukas1051

18

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.

Reply 90

silvertear

1

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 :s-smilie:

Reply 91

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?

Reply 92

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 :s-smilie:

technically yes, but in practice collisions are inelastic.

Reply 93

xiyangliu

2

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

This was posted from The Student Room's iPhone/iPad App

Reply 94

silvertear

1

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?

Reply 95

PhysicsGirl

OP

7

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.

Reply 96

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? :confused:

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?

(edited 11 years ago)

Reply 97

PhysicsGirl

OP

7

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/physics/html/helpforstudents.html

Reply 98

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? :confused:

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? :smile:

(edited 11 years ago)

Reply 99

Amy-Rose

8

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?

OCR ADVANCING PHYSICS B G494 EXAM MONDAY 18th June

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