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OCR PHYSICS B G492~ 9rd June 2014~ AS Physics Watch

1. Btw, do we give answers to 2 sig fig or 3 sig fig? All mark schemes show 2 sig fig except the june 2013 mark scheme which shows 3 sig fig. So confused
2. (Original post by shloke123)
Btw, do we give answers to 2 sig fig or 3 sig fig? All mark schemes show 2 sig fig except the june 2013 mark scheme which shows 3 sig fig. So confused
I'm pretty sure that as long as you go for 2 or 3 significant figures you'll be fine! They quite often give the answer in both. If you want to be on the safe side, look at the significant figures of the values they provide you in the question and then make a judgement based on that for your answer.
3. (Original post by shloke123)
Btw, do we give answers to 2 sig fig or 3 sig fig? All mark schemes show 2 sig fig except the june 2013 mark scheme which shows 3 sig fig. So confused
Give it to the lowest level of precision that is given in the question. OCR is hideously inconsistent with their significant figures but as long as you stick to the lowest level of precision (which will generally be 2sf), you'll be fine.
4. Can I have a link to the resource booklet? I can't seem to find it.
5. Does anyone know how to choose the right graph for question like
y axis- energy of photon of electromagnetic radiation
x axis - the frequency of radiation
6. (Original post by LimbuRonit)
Does anyone know how to choose the right graph for question like
y axis- energy of photon of electromagnetic radiation
x axis - the frequency of radiation
First I'd think about or write down the equation that links them. In this case it is E=hf. So as f increases, E increases. So the graph is linear as there is a linear relationship between them.
For kinetic energy E=1/2mv². As v increase E goes up by the square of this. So it will be a curve with an increasing gradient, or y=x² roughly.
If you want the graph of wavelength against E, you have E=hc/λ. So as λ increases, E decreases. As λ tends to 0, E will become infinitely big, so you have a curve with an increasing gradient that tends to 0 but does not ever reach it, like y=1/x.
Those are the 3 main shapes, I hope that makes sense.
7. (Original post by uncleniccius)
Can I have a link to the resource booklet? I can't seem to find it.
http://www.ocr.org.uk/Images/77851-d...91-to-g495.pdf
8. (Original post by MasterOfTheSwag)
First I'd think about or write down the equation that links them. In this case it is E=hf. So as f increases, E increases. So the graph is linear as there is a linear relationship between them.
For kinetic energy E=1/2mv². As v increase E goes up by the square of this. So it will be a curve with an increasing gradient, or y=x² roughly.
If you want the graph of wavelength against E, you have E=hc/λ. So as λ increases, E decreases. As λ tends to 0, E will become infinitely big, so you have a curve with an increasing gradient that tends to 0 but does not ever reach it, like y=1/x.
Those are the 3 main shapes, I hope that makes sense.
ohh i see now. can you help me with a question?
A stone is thrown vertically upwards at 12 ms^-1.

Calculate the speed of v of the stone when it is 3m above the point of prejection.
g=9.81

the correct formula is v^2=u^2 + 2as
v^2=12^2+2(-9.8)(3)

why is the g= minus ?
9. (Original post by LimbuRonit)
ohh i see now. can you help me with a question?
A stone is thrown vertically upwards at 12 ms^-1.

Calculate the speed of v of the stone when it is 3m above the point of prejection.
g=9.81

the correct formula is v^2=u^2 + 2as
v^2=12^2+2(-9.8)(3)

why is the g= minus ?
Right it has a velocity of 12m/s upwards. Gravity is acting in the opposite direction, so you could say it is accelerating it down at 9.8m/s², or say it is accelerating it up at -9.8m/s², if that makes sense. It's basically to do with the fact that the initial velocity and gravity are happening in opposite directions, so one direction is positive, the other is negative. I don't know how to explain it better than that really.
10. Thank you!
11. How do you calculate %uncertainty in g once you have max/min values??

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12. In terms of sig figs, unless there is a clear indication otherwise, stick to 3sf and you will never be penalised. The exception is uncertainty, where you must always go to 1sf fewer than the measurements (unless the measurements are 1sf, obviously).

I hope standing waves don't come up, I find then the most difficult part of this topic because you're never exactly sure what the question is asking you to explain. And bring on the mechanics! I did M2 for further maths a couple of weeks ago so physics mechanics seems peachy!
13. (Original post by emfp21)
How do you calculate %uncertainty in g once you have max/min values??

Posted from TSR Mobile
If you were given that a ruler is 30 +/- 0.1cm long then it would be (0.1*100)/30
14. (Original post by blackwatersun)
In terms of sig figs, unless there is a clear indication otherwise, stick to 3sf and you will never be penalised. The exception is uncertainty, where you must always go to 1sf fewer than the measurements (unless the measurements are 1sf, obviously).

I hope standing waves don't come up, I find then the most difficult part of this topic because you're never exactly sure what the question is asking you to explain. And bring on the mechanics! I did M2 for further maths a couple of weeks ago so physics mechanics seems peachy!
Yeah standing waves are a nightmare! What they want in the mark scheme is always so specific. In general though if you talk abut two waves in opposite directions and mention interference you'll get a few marks.
15. Standing waves is pretty straight forward I though? I always write (using string as example) wave travels along string, reflected at the end of string, two waves created with directions of travel in opposite directions, since waves are from the same source they are coherent, when they pass through each other they superimpose, where constructive interference occurs antinodes are formed and where destructive interference occurs, nodes are formed. That pretty much guarantees full marks
16. (Original post by emfp21)
How do you calculate %uncertainty in g once you have max/min values??

Posted from TSR Mobile
Difference between max or min min value and the mean value, divided by the mean value, multiplied by 100
17. I like standing waves apart from one bit - how do you do it when they ask you about one that is say 3 x the fundamental frequency etc?

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18. (Original post by Carla Huynh)
Yeah standing waves are a nightmare! What they want in the mark scheme is always so specific. In general though if you talk abut two waves in opposite directions and mention interference you'll get a few marks.
In phase and out of phase seems to consistently be in the mark schemes, and works for standing waves and superposition in general.
19. Does anyone have the June 2013 paper for physics B? I need it.
20. (Original post by emfp21)
I like standing waves apart from one bit - how do you do it when they ask you about one that is say 3 x the fundamental frequency etc?

Posted from TSR Mobile
Does fundamental frequency normally have one loop or something? I just tend to work it out using whatever fraction of the wavelength it is, or something along those lines. So one loop would be lamda/2?

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