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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 mnasmith)
can someone tell me how to do this question please?
Attachment 222375 answer is c but how?
ignore the attatchment just the picture is necessary

The EMF of the circuit is 9V. There are only 2 components in the circuit because internal resistance is negligible. Therefore the voltage of the 2 components must be equal to 9V (because the total energy dissipated per coulomb through the circuit must be equal to the total energy gained per coulomb at the battery). Then you use the graph to see what current gives a total voltage of 9 volts when component ones voltage is added to component 2's, the answer being C, 3 Volts + 6 volts.

That might not be too clear but I'm not too good at explaining things, let me know if there is anything you want clarified.
2. Could somebody explain the answer to Jan 2010 Q20 part b)
3. Also, June 2010 Q13 part b) , to be on the safe side
4. i Still dont understand in JUNE 2011 QUESTION 15ciii how to do it! its imposible!
5. (Original post by KBenzema)
i Still dont understand in JUNE 2011 QUESTION 15ciii how to do it! its imposible!
The resistance would increase once removing the lamp because they are in parallel. Do it yourself, using 1/R+1/R. And because V=IR there would be increase in p.d for P.
6. (Original post by KBenzema)
i Still dont understand in JUNE 2011 QUESTION 15ciii how to do it! its imposible!
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.
7. (Original post by Zoeyyy)
Also, June 2010 Q13 part b) , to be on the safe side
Thermistor resistance increases. By V=IR with I constant, pd across thermistor increases, so voltmeter reading decreases since pd across thermistor =pd across 1000 ohms resistor.
8. Hello, can anyone explain to me why the answer to this question is A and not B?
9. (Original post by FarmerMan)
Hello, can anyone explain to me why the answer to this question is A and not B?
Go a few pages back.
10. (Original post by FarmerMan)
Hello, can anyone explain to me why the answer to this question is A and not B?
Well basically using the equation I=V/R, you can see that it is a reciprocal graph of the form y=1/x. That's how I see it anyway.

Can someone explain to me when working out the radiation flux why we use the height of the light source as the radius (to calculate area)? It doesn't come intuitively to me, I don't get it. Thanks!

Incase anyone wants an example Jan 09 Q19 a). You're given power:60 W (5% efficiency), height:2.5m, and made to assume area 4.pi.r^2
11. Hey.can someone post jan 2013 paper with mark scheme.

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12. (Original post by blacknightking)
Hey.can someone post jan 2013 paper with mark scheme.

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http://www.mediafire.com/?5djntd8dd7ykb
13. (Original post by LegendX)
Anyone?
if there is 12V on the first strand, shouldn't there just be 12V on the second?
tried this so many times, so many calculations, and this is the only conclusion i could come too.
ARGH.
14. could someone explain the very last question on the june09 paper?
http://www.edexcel.com/migrationdocu...e_20090521.pdf
thankyou..
15. (Original post by LegendX)
Anyone?
Hi
well you know that the voltage across the first branch is 12 V
this means that the voltage across the other branch is also 12 V
Remember, In parallel circuits the pd across each component is the same :P
that means that the pd across the resistor (R1 if I recall correctly) is 3V
now you should be able to finish off the questions .. I did this question today :P
16. (Original post by ellanokesy)
if there is 12V on the first strand, shouldn't there just be 12V on the second?
tried this so many times, so many calculations, and this is the only conclusion i could come too.
ARGH.
Yep that's it
so the p.d. across R1 is 3V
17. Can someone expalin 15 b in 2010 paper below? Link below: Thanks!

http://www.edexcel.com/migrationdocu...e_20100118.pdf
18. (Original post by x0x)
Yep that's it
so the p.d. across R1 is 3V
YES!
thats what i got. i was doing so many complicated calculations then realised for 1 mark, it was so simple i was just missing the boat!
thank you
19. Alright. Guys. June 2009 Q 20 b i)

I understand that it is described as being a standing wave in the mark scheme, but how is this possible if the wavefronts are open to the elements ? Please explain? Thank you.

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20. http://www.edexcel.com/migrationdocu...e_20100118.pdf
can someone help me with 19c)ii
thankyou x

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