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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 GCSE-help)
I put D but unfortunately I've realized it must be C The question doesn't tell us which way the wave is moving, it is a displacement TIME graph. We can't use the 'tracing' method, so yeah we were tricked

The only possible option is C
Can you elaborate further?
i don't really see what you mean. If it was a displacement time graph you cannot work out the wavelength which would explain why my method is incorrect, leaving C as the only possible answer but there has to be a better explanation ?
2. (Original post by x0x)
Can you elaborate further?
i don't really see what you mean. If it was a displacement time graph you cannot work out the wavelength which would explain why my method is incorrect, leaving C as the only possible answer but there has to be a better explanation ?
Well that was not describing the wave.
The graph was describing the (simple harmonic) oscillations of one point in the wave to another, so hence displacement vs time

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3. (Original post by x0x)
The one about S and O (one is a source the other is an observer)
i think the answer is C .. both move towards each other so frequency increases?
I put the option with S and O in opposite directions which said that frequency decreases! Wasn't there such an option?
4. (Original post by Alexsk)
I put the option with S and O in opposite directions which said that frequency decreases! Wasn't there such an option?
my bad! there was only one option with both going towards each other :P it doesn't matter hehe
5. My MAIN concern is the last question. Does anyone have any clue what the hell the answer was? Can't believe it's been this long after the exam and there's so much disagreement over the answer. No textbook or internet source seems to be helping
6. 1)Because it was a lamp I think it behaves like a filament lamp. As current decreases, heat decreases.
2) Therefore, the energy provided to ions decreases. Vibrations of ions decreases.
3)Less collisions with electrons.
4)Less resistance
7. (Original post by Alexsk)
1)Because it was a lamp I think it behaves like a filament lamp. As current decreases, heat decreases.
2) Therefore, the energy provided to ions decreases. Vibrations of ions decreases.
3)Less collisions with electrons.
4)Less resistance
Now are you SURE about this? Have you had it confirmed by teachers etc etc. Because this is what I put and EVERYONE seems to disagree back in school. If it's right, I'm gonna be so happy.
8. (Original post by StephenNaulls)
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.

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Right on, i remeber that question now, i think the 1322.5 came from the resistance of the bulb later on in the exam
9. (Original post by Alexsk)
1)Because it was a lamp I think it behaves like a filament lamp. As current decreases, heat decreases.
2) Therefore, the energy provided to ions decreases. Vibrations of ions decreases.
3)Less collisions with electrons.
4)Less resistance
What about voltage? Shouldn't the sum be equal to 230!!!!!!!!!

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10. (Original post by StUdEnTIGCSE)
What about voltage? Shouldn't the sum be equal to 230!!!!!!!!!

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No because it was being operated at below it's normal rating! I think people are missing a massive key point. The question asked for the effect of low current ON the resistance. So it's not asking us to consider WHY the current was low, just accept that it was! And then we had to find the effect of the low current on the resistance!
11. (Original post by GCSE-help)
Now are you SURE about this? Have you had it confirmed by teachers etc etc. Because this is what I put and EVERYONE seems to disagree back in school. If it's right, I'm gonna be so happy.
i wrote this and most of my classmates disagree
12. 99% sure. The lamp is definitely not an ohmic resistor. Therefore R is not inversely proportional to I. Moreover, it cannot be a diode- semiconductor. So what is left? The filament lamp!!!

13. Right on, i remeber that question now, i think the 1322.5 came from the resistance of the bulb later on in the exam
Yeah, I think that's what i got too. I remember getting a little worried because it was such a high resistance and quite a weird number. I'm used to them giving us a "normal" number like the 12.5 one we got just after!
14. I feel like they could've worded this last question so much better. I know the theory behind resistance in a filament lamp. If that was what they wanted they should have made it clearer!!!
15. (Original post by Alexsk)
99% sure. The lamp is definitely not an ohmic resistor. Therefore R is not inversely proportional to I. Moreover, it cannot be a diode- semiconductor. So what is left? The filament lamp!!!
are u alex from xtremepapers? :P
16. (Original post by StephenNaulls)
I feel like they could've worded this last question so much better. I know the theory behind resistance in a filament lamp. If that was what they wanted they should have made it clearer!!!
ya it was kinda of tricky
17. so the 3rd MCQ is it D or C ?
18. (Original post by StephenNaulls)
I feel like they could've worded this last question so much better. I know the theory behind resistance in a filament lamp. If that was what they wanted they should have made it clearer!!!
Agreed, edexcel has a habit of badly worded questions
19. (Original post by hamzeh h)
so the 3rd MCQ is it D or C ?

20. Right on, i remeber that question now, i think the 1322.5 came from the resistance of the bulb later on in the exam
I got the same that's another 1 mark

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Updated: December 18, 2013
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