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# Edexcel Physics Unit 2 "Physics at work" June 2013 Watch

• View Poll Results: The last question - Does resistance increase or decrease?
It increases ( using V=IR or some other method)
70.73%
It decreases using the 'lattice vibrations' theory
29.27%

1. (Original post by awesomesoccerfan)
I referred to the equation R=(rho x l)/A and said that R is inversely proportional to A and directly proportional to l.As l increases and A decreases so R would be higher.Am i right?
I said that as well, it should be right
2. What did people put for question 10, which is not involved in this, i ticked polarisation, because reflection, refraction, and superposition were all happening
3. (Original post by Mo_maths)
What did people put for question 10, which is not involved in this, i ticked polarisation, because reflection, refraction, and superposition were all happening
yepp ... polarization does happen but it is not involved in the interference pattern
4. As for the last question
I think it was a series circuit
I did a calculation to see what current would flow through the circuit if it was a series one and I got a value of 0.2 A which is exactly what is needed for the lamps .. did that ofc after finishing the question
On the whole it was a good paper but electricity was a bit tricky
5. (Original post by x0x)
yepp ... polarization does happen but it is not involved in the interference pattern
so is it correct?
6. (Original post by GCSE-help)
Hi guys. Thought it was a good paper, until it got to the last question I put resistance would be lower at a lower current because of less heating, so fewer ionic vibrations and less electron-ion collisions. Seems like I was in the minority. Thoughts?
I said this as well.
7. (Original post by JoshThomas)
I put resistance would be lower for the same reasons you did and in series

Posted from TSR Mobile

(Original post by GCSE-help)
Series, because if one bulb went out the other one did too.
I put series as well

It helps so much theref you treat one bulb as a switch
8. (Original post by krisshP)
I said this as well.
I said that I decreases
so for a given voltage the resistance should increase
since V=IR
but its true ... when current decreases there is less heating but I depended on the equation since there were 4 marks and in mark schemes they almost always require you to quote a relevant equation :P
9. (Original post by jollygood)
For last Mcq I put polarization. and for one with angle of incidence and angle or refraction I did 90- whatsoever the angle with horizontal. and angle of refraction was smaller value.

(Original post by GCSE-help)
I got mgh/VIT for the efficiency, even though some said it was 0.5mv^2/VIT.

I also put superposition for the final MC but apparently it was polarisation. Silly me for not reading the q
wtf

It is polarisation. Reflection was present

http://www.physicsclassroom.com/clas...2l1e.cfm#refln

So polarisation was present as there's polarisation by reflection.
10. (Original post by krisshP)
I said this as well.
i dont think it wanted you to put that, i thought about it but read the question over and over a few times then decided against it, you had to use equations such as V=IR
11. Can someone please draw the circuit for the q on the mains and two bulbs?
Thanks
12. (Original post by krisshP)
wtf

It is polarisation. Reflection was present

http://www.physicsclassroom.com/clas...2l1e.cfm#refln

So polarisation was present as there's polarisation by reflection.
Why does petrol and oil make a rainbow effect on water?

This is because the oil spreads out to form a very thin film on
the surface of the water, but of varying thickness. In some places it is literally a molecule thick, whilst in other places it is much thicker. When light passes through the oil some of it is reflected back off the different layers of oil, whilst some carries on and is reflected off the surface of the water lying below. Because the light waves have now travelled different distances before being reflected they mix together producing a spectrum of colours - because the thickness of the oil layer varies. For the super intelligent the light spectrum occurs because, having travelled slightly different distances, some of the waves are now 'out of phase' and cancel each other out, producing dark spots, whilst others add together, producing lighter spots. And refraction because the light moves from oil to water then light ext
13. (Original post by Mo_maths)
i dont think it wanted you to put that, i thought about it but read the question over and over a few times then decided against it, you had to use equations such as V=IR
so you think R increases
as for the photon question , the one worth 2 marks .. I said
A photon is a discrete quantum of electromagnetic radiation
is this good enough for 2 marks?
and for the polarization question I said:
The wave oscillates only in one plane perpendicular to its direction of propagation. Only transverse waves can be plane polarized ( and I drew a diagram of oscillations in one plane perpendicular to the direction of movement)
As for the corrosion question I got a value of 1.5 cm .. is that what you got?
Yes I did, bloody annoying. That's the way the papers seem to be going. It's crap because you have to spend longer writing wordy answers and then you have less time to check over. But you also have to spend longer checking over! Sucks. Plus I love maths.

By the way, what did everyone put for a 3 mark question on defining plane polarised light? 3 marks??!! I think I said oscillates in one plane only, transverse and can be achieved using a polarising filter.
And two marks for defining a photon? I said it was a particle used to describe light, and that it was a discrete packet of energy or something like that.
Oscillations in a single direction [1] which is perpendicular to direction of wave propagation[2] it was a 2 mark q.

Packet of energy [1] which has discrete specific energy [1] was a 2 mark q as well
15. (Original post by x0x)
so you think R increases
as for the photon question , the one worth 2 marks .. I said
A photon is a discrete quantum of electromagnetic radiation
is this good enough for 2 marks?
and for the polarization question I said:
The wave oscillates only in one plane perpendicular to its direction of propagation. Only transverse waves can be plane polarized ( and I drew a diagram of oscillations in one plane perpendicular to the direction of movement)
As for the corrosion question I got a value of 1.5 cm .. is that what you got?
Yes!
16. (Original post by Mo_maths)
Yes!
So you think there is a good chance that I will get full marks in these parts?
17. (Original post by GCSE-help)
Someone put the Unit 1 paper on here very quickly this year, hope they do the same with this paper if it's possible!

I think for the last one the question asked us the effect of low current on the resistance of the bulb, so it wasn't asking for us to use any formulas, but use the fact the temperature would be less due to less current, so the ions in the lattice would have less energy and vibrate less, leading to less electron-ion collisions etc etc, so the resistance would reduce. That's what usually happens when a lamp is operating below it's normal rating, there is a low resistance which could give rise to a huge surge in current momentarily if a significant potential difference is applied

(Original post by nukethemaly)
I said it would increase. I actually tried this on the calculations too, just to make sure it made sense, like, I lowered the current and the resistance did increase
Current causes a heating effect, so lower current means lower temperature of wire. Hence atomic vibrations decrease and since these atomic vibrations impede current, lower wire temperature causes a lower frequency of collisions between atoms and electrons. So resistance decreases with lower current.

Wrong or right? I think logically it makes sense.
18. (Original post by GCSE-help)
Someone put the Unit 1 paper on here very quickly this year, hope they do the same with this paper if it's possible!

I think for the last one the question asked us the effect of low current on the resistance of the bulb, so it wasn't asking for us to use any formulas, but use the fact the temperature would be less due to less current, so the ions in the lattice would have less energy and vibrate less, leading to less electron-ion collisions etc etc, so the resistance would reduce. That's what usually happens when a lamp is operating below it's normal rating, there is a low resistance which could give rise to a huge surge in current momentarily if a significant potential difference is applied

Look above, that's exactly what I said.

So how come by formulae V=IR it can't make sense this explanation?
19. (Original post by krisshP)
Current causes a heating effect, so lower current means lower temperature of wire. Hence atomic vibrations decrease and since these atomic vibrations impede current, lower wire temperature causes a lower frequency of collisions between atoms and electrons. So resistance decreases with lower current.

Wrong or right? I think logically it makes sense.
thats exactly what i said some people disagreed
20. (Original post by x0x)
So you think there is a good chance that I will get full marks in these parts?
i recon so

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