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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 B-Stacks)
Yes, if you know the the EMF and two Resistance values of the resistors.
What I mean is , which method awards the full marks.

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2. (Original post by blacknightking)
What I mean is , which method awards the full marks.

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Either way usually. But they'd expect you to apply your knowledge of potential dividers by using the formula.
3. Help needed with jan 2011 question 5

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4. Can someone help me with question 9, about I=nqva on june 2012 paper. link below: Thanks!

http://www.edexcel.com/migrationdocu...e_20120525.pdf

Why is the answer 1/2 and not 2? Surely the drift velocity doubles when area has been doubled.
Therefore Speed of A/Speed of B = 2. But its not...help!
5. (Original post by blacknightking)
Help needed with jan 2011 question 5

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The filament of M breaks. This means that the lamp in p-arallel is effectively removed. Now we have a bulb that was previoussly in parallel in series. When in parralel the resistance across the bulbs as a whole was lower (1/RT=1/R1+1/R2 etc.) but now the bulb is in series the resistance has increased. The total EMF stays constant so the voltage across the whole circuit is still the same. As the resistance has increased, looking at the equation V=IR we can see that the current must have decreased. We know that P=IV and that Voltage is split in a circuit equal to the ratio of the resistances. The lamp now has more resistance compared to before and so is a larger proportion of the total resistance than before , and hence takes more of the voltage. The lamp N is now a smaller proportion of the total resistance than it was before and so takes less P.D. P=IV and a greater V for the first lamp than previously and a smaller V for lamp N shows that the power will increase and decrease respectively.
6. (Original post by Jaydude)
Can someone help me with question 9, about I=nqva on june 2012 paper. link below: Thanks!

http://www.edexcel.com/migrationdocu...e_20120525.pdf

Why is the answer 1/2 and not 2? Surely the drift velocity doubles when area has been doubled.
Therefore Speed of A/Speed of B = 2. But its not...help!

They are in series and therefore they have the same current:

I=nAvq ~ If I is to stay the same whilst A has been doubled, its obvious that to offset this one of the other variables must be halved to maintain the same current. We are talking about A , so the Drift velocity of A will now be 0.5 its original drift velocity and the current has stayed constant. Now the ratio would just be the velocity of A over the velocity of B. 0.5v/1v = 0.5. Half anything over one of something will always be half.
7. (Original post by Jaydude)
Can someone help me with question 9, about I=nqva on june 2012 paper. link below: Thanks!

http://www.edexcel.com/migrationdocu...e_20120525.pdf

Why is the answer 1/2 and not 2? Surely the drift velocity doubles when area has been doubled.
Therefore Speed of A/Speed of B = 2. But its not...help!
I = nqvA which means that v = I/nqvA
So when x-sectional area is doubled, CURRENT doubles, but the drift velocity doesn't - it halves.
Hope this helps
8. Can someone help me with question 10, about diffraction on January 2013 paper.:

The effect of diffraction is more noticeable, in everyday life, with sound than with light. This is because
A sound has a much longer wavelength than light
B sound is a longitudinal wave, light is a transverse wave
C sound is a mechanical wave, light is an electromagnetic wave
D sound travels more slowly in air than light does

9. (Original post by kitty-boo)
Can someone help me with question 10, about diffraction on January 2013 paper.:

The effect of diffraction is more noticeable, in everyday life, with sound than with light. This is because
A sound has a much longer wavelength than light
B sound is a longitudinal wave, light is a transverse wave
C sound is a mechanical wave, light is an electromagnetic wave
D sound travels more slowly in air than light does

We know that light has a very small wavelength. In order to see diffraction we would need light to pass a really small gap/object which is approximately the same size as its wavelength. So it's highly unlikely for us to see this.
10. (Original post by kitty-boo)
Can someone help me with question 10, about diffraction on January 2013 paper.:

The effect of diffraction is more noticeable, in everyday life, with sound than with light. This is because
A sound has a much longer wavelength than light
B sound is a longitudinal wave, light is a transverse wave
C sound is a mechanical wave, light is an electromagnetic wave
D sound travels more slowly in air than light does

Because of a longer wavelwngth the dustanxe between each wavefront is longer rherefore us easier to see. That question confused my class too dw.

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11. (Original post by CharlieTT)
Because of a longer wavelwngth the dustanxe between each wavefront is longer rherefore us easier to see. That question confused my class too dw.

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(Original post by B-Stacks)
We know that light has a very small wavelength. In order to see diffraction we would need light to pass a really small gap/object which is approximately the same size as its wavelength. So it's highly unlikely for us to see this.
Thank you!
12. (Original post by kitty-boo)
Can someone help me with question 10, about diffraction on January 2013 paper.:

The effect of diffraction is more noticeable, in everyday life, with sound than with light. This is because
A sound has a much longer wavelength than light
B sound is a longitudinal wave, light is a transverse wave
C sound is a mechanical wave, light is an electromagnetic wave
D sound travels more slowly in air than light does

Diffraction is the bending of a wave that occurs when a wave travels through a gap. The amount of diffraction is dependent on the wavelength of the wave relative to the size of the gap. If the wavelength is a similar size to the gap it will undergo diffraction and the light will bend, if you have the same gap but a wave that has a wavelength much smaller then the wave will be much smaller in size relative to the gap and will pass through will less diffraction. A good thing to thing about when visualizing diffraction is light and sound. We can hear around doors because the wavelength of sound is similar in size relative to the gaps and therefore sound bends round the corners allowing it to be heard even when not directly in the line of sight, the wavelength of light on the other hand is very small and is much smaller than the gap, it therefore undergo's very little diffraction and doesn't bend, so you must be in the Line of sight to see it.

Back to the question, the longer wavelength of sound means it is similar in size relative to the gaps encountered in the world and therefore diffracts more, the much smaller wavelength of light means it is often much smaller than gaps it passes through and undergoes no observable diffraction.

Hope that helped.
13. I cant get the unit 2 paper! Ffs. Its a unit 1 paper that i can only find, wheres unit 2?!? The link was for unit 1 paper

EDIT: nevermind
14. (Original post by cwe)
here goes:

As we know, 2 resistors in parallel have less resistance than they would have if they were connected in series. 1/r1 + 1/r2 + 1/r3 = 1/total resistance. When this lamp is removed resistors that were in parallel and hence each had a lower resistance now have a greater resistance. The circuit without the lamp is effectively a series circuit in which current is split amongst components based on the proportion of the total resistance they represent. This component will have a larger resistance, will therefore receive a larger proportion of the voltage and the voltmeter will therefore read a larger value for the potential difference.
thank you! Brilliant!
15. I never actually checked the link, i wanted the paper as a mock. But Im trying to look for it and the link only has unit1 2013 jan papers....Wheres Unit 2!?!?

EDIT: nevermind , got it. Checked every PDF which were labblled as "6ph01" and got it. Please make titles more clearer next time!
16. Energy loss depends on Current,Resistance or Power? when do we know if teres greater or smaller energy loss?
17. Energy loss depends on Current,Resistance or Power? when do we know if *theres greater or smaller energy loss?
18. (Original post by KBenzema)
Energy loss depends on Current,Resistance or Power? when do we know if *theres greater or smaller energy loss?
I believe it is essentially power. If something was to loose 3j/s it would be the same principal as using 3j/s, if that makes sense. P=IV so the power is dependant on those things, but you have to look at the power to get a decisive answer.
19. Anyone who can please explain potential dividers?
20. Can someone please explain to me how to do Q 7 and 14 ( in depth tutorial please)

http://www.edexcel.com/migrationdocu...e_20120307.pdf

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