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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 Superhans34)
I used V=IR, meaning the resistance increases (as it doesn't mention anything about temperature I didn't want to include that in my explanation). Because the resistance increases, as P=VI, P decreases meaning the bulbs don't light because more electrical energy is wasted/dissipated due to the increased resistance. So less goes through the bulbs.

Don't know if that is right though but I think it makes sense.

also it doesn't anything about a filament lamp so I didn't put that in my answer because for all we know it could have been fluorescent which isn't affected by temp etc. I think it could have been worded better
but in the picture its a filament lamp fluorescent lamps has a different shape tube like
2. (Original post by hamzeh h)
but in the picture its a filament lamp fluorescent lamps has a different shape tube like
If it was important, don't you think they would state it rather than expecting you to deduce what lamp it is from a picture?
3. (Original post by a10)
what did u put for the multiple choice question for the refraction angle?

angle of incidence was 33 degrees and was the refraction one 21 degrees (or was it the one with 55 degrees) ?
yes I chosed A.

90-57=33

and the angle of refraction should be less than that as it is bent towards the normal as it enters the more optically dense glass so got to be 21 not 55
4. (Original post by a10)
I put 33 and 21 as well, but looking at the diagram its confusing it looks like more dense to less dense which would mean its 33 and 55....but from the left that must be air so at the same time I think our answer was correct
but its not very ambiguous...even if you considered the second refraction

https://www.dropbox.com/sh/v6ydqbfrg...H?lst#f:q7.JPG
5. (Original post by StUdEnTIGCSE)
but its not very ambiguous...even if you considered the second refraction

https://www.dropbox.com/sh/v6ydqbfrg...H?lst#f:q7.JPG
okay that's good caz I chose A too, I was just panicking now wen looking at the pic
6. Anyone knows why energy cannot accumulate in an atom ...so that any frequency light even if it was less than threshold frequency would cause PE emission.??
I dont get why.. electrons can jump one by one to the higher levels and then get emitted????
Or is absortion transitions only restricted to ground state of the electrons ??
7. (Original post by TheKingOfTSR)
Anyone knows why energy cannot accumulate in an atom ...so that any frequency light even if it was less than threshold frequency would cause PE emission.??
I dont get why.. electrons can jump one by one to the higher levels and then get emitted????
Or is absortion transitions only restricted to ground state of the electrons ??
I thought a photon was emitted, not an electron.
8. (Original post by Alexandra82)
I can remember the exact value that i got for the critical angle, but it was around 47 or 48... did anyone get the same?
Yep, It was Sin-1(1/1.33) which i believe was 48.8
10. Answers i got for the Maths questions:

1322.5 (smoewhere perhaps wavelength?)
0.17 (electricty q (the last question) )
12.5 ( Last question again)
48.8 (Critical angle)
1.04*10^15 (Photon Question)
16.9 (somewhere)
1.5 cm for the corrosion question)

Similar results anyone?

11. Answers i got for the Maths questions:

1322.5 (smoewhere perhaps wavelength?)
0.17 (electricty q (the last question) )
12.5 ( Last question again)
48.8 (Critical angle)
1.04*10^15 (Photon Question)
16.9 (somewhere)
1.5 cm for the corrosion question)

Similar results anyone?
ya same the 1322 was the value of resistance for the large bulb
12. (Original post by hamzeh h)
Hmm not sure , but my friends found it an easy exam, did your school find it easy?
13. (Original post by Superhans34)
I used V=IR, meaning the resistance increases (as it doesn't mention anything about temperature I didn't want to include that in my explanation). Because the resistance increases, as P=VI, P decreases meaning the bulbs don't light because more electrical energy is wasted/dissipated due to the increased resistance. So less goes through the bulbs.

Don't know if that is right though but I think it makes sense.

also it doesn't anything about a filament lamp so I didn't put that in my answer because for all we know it could have been fluorescent which isn't affected by temp etc. I think it could have been worded better
I wrote the same as you and my reasoning for it is the same as yours. It didn't make it clear it was a filament lamp (did it even say it?) so we can't be expected to decide for ourselves whether its fluorescent or fillament. Therefore, to me, it made sense to use Ohm's Law. Even more so since the conditions were constant.

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14. Guys you're forgetting it's not 'how easy people found it' that determines the grade boundaries, it is how well (in terms of marks) we actually did! I remember a Bio exam in Jan, which everyone came out feeling super confident over, but then the grade boundaries were so low and a lot of people flopped.

I personally think it will be 55 for an A.
15. (Original post by Superhans34)
I thought a photon was emitted, not an electron.
A photoelectron is emitted.

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16. (Original post by GCSE-help)
Guys you're forgetting it's not 'how easy people found it' that determines the grade boundaries, it is how well (in terms of marks) we actually did! I remember a Bio exam in Jan, which everyone came out feeling super confident over, but then the grade boundaries were so low and a lot of people flopped.

I personally think it will be 55 for an A.
I agree that sometimes we can think that it is an easy exam and yet grade boundaries are low but usually if the exam is easy we shoud all do well

17. Answers i got for the Maths questions:

1322.5 (smoewhere perhaps wavelength?)
0.17 (electricty q (the last question) )
12.5 ( Last question again)
48.8 (Critical angle)
1.04*10^15 (Photon Question)
16.9 (somewhere)
1.5 cm for the corrosion question)

Similar results anyone?
I think your first answer is incorrect. The frequency was 216.8 MHz(around) so it had to be converted to 10^6 Hz and the powers cancelled to give just over 1m wavelength.

Posted from TSR Mobile
18. was this exam hard or easy guys?? i dont do this...but damn i did the physics unit 1 exam and it ruined my life..
19. (Original post by StephenNaulls)
A photoelectron is emitted.

Posted from TSR Mobile
Yeah during the photoelectric effect but when the electron just jumps between an energy level, the energy lost is emitted as a photon. Not a photo-electron/electron because that doesn't make sense.
20. Guys do we think the final answer was a decrease or an increase in resistance? I firmly believe it is a decrease. I don't think you can use ohm's law because it was a series circuit so V is not the same across each lamp. They also said the bulbs didn't light up which was a clue. A MASSIVE clue was they asked us for the effect of low current ON the resistance, they didn't ask us to explain an increase/decrease in resistance USING the low current. Do you guys kinda get what im trying to say?

Therefore I believe it was the lattice vibrations argument. It doesn't make sense to have 4 marks on an equation derivation question either imo.

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Updated: December 18, 2013
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