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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 krisshP)
Just remember for refraction his analogy in Khan academy
Hi can you please look at the two questions I just posted and see if you can help me with them
2. Who completed the loads of questions on scribd?
I am on my way through it. 3/4 to go.Not sure whether it is important to do them or do some other revision.

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3. (Original post by JoshThomas)
What do you mean divided by resistances?

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I would crop/print screen if I knew how, but... Oh wait - here :

EDIT: I just realised, that's the potential divider formula, isn't it?

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4. (Original post by Branny101)
I would crop/print screen if I knew how, but... Oh wait - here :

EDIT: I just realised, that's the potential divider formula, isn't it?

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Yeaa potential divider formula , output voltage= terminal pd × ( resistance across component for which you want the voltage across so 1000/ sum of resistors so 1000+ 1300) yaa

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5. (Original post by JoshThomas)
Okay so potential difference is split between components, so you need to find where voltage across resistor + voltage across bulb = 9 v and also the current has to be the same for these voltages, so by inspection looking on the graph, when the voltage across the resistor is 6 and the voltage across the bulb is 3, and thr current is 0.3amps for both, and 6 + 3=9
ohhhhh!
6. (Original post by JoshThomas)
Yeaa potential divider formula , output voltage= terminal pd × ( resistance across component for which you want the voltage across so 1000/ sum of resistors so 1000+ 1300) yaa

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Ahhh awesome duuude

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7. (Original post by JoshThomas)
2). Find the resistance of the paralell combination, : 1/200+ 1/200= 1/R gives R is 100, so the first resistor has 200 and the combination of the next 2 is 100, voltage get split between components and the ratio of this voltage split will be the same as the ratio of the resistors which in this case is 2:1, since the terminal p.d is 12v, you have to split this in the ratio 2:1, so 8:4, leaving 4 volts as the p.d across the paralell combination

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naw thankyou so much :c
8. anyone puleez give me a detailed explanation of phase and path difference????
9. Student did a beautiful explanation a few pages back.

(Original post by StUdEnTIGCSE)
Well phase difference is the fraction of difference of oscillation of one oscillator to another. It measured as an angle in radians or in degrees. It actually sees how the sine curve of one wave has been translated to get another along the x axis. A translation or phase difference of 0,2π,4π
...2nπ (multiples of 2π) gives the same curve back again so its thought to be in phase, while a phase angle difference of π,3π....2n+1π gives a sine curve that is totally opposite so its out of phase.
You can work with degrees also.

Path difference is the difference in the distance travelled between two waves from their source. It can be measured as distance or in wavelength. If the difference shows a multiple of one wavelength they are in phase while a odd multiple of half wavelengths(0.5lamda,1.5lambda) shows an exactly out of phase points in the two wave. The significance of this can be seen in the principle of superposition of waves, diffraction and interference patterns etc

The relationship between these two variables are simple. A phase angle difference of 2π or 360° corresponds to 1 lambda path difference so use this ratio method

Spoiler:
Show

You can substitute for path difference or wavelength to find for the other. Use the lambda and the 2π as numbers which can be cancelled.
10. (Original post by pureandmodest)
Cell voltage is 9V. Sum of emfs=sum of pd across components in series. So 9V=pd across 20 ohms resistor +pd across lamp. So you must find the point on the graph where pd across 20 ohms resistor +pd across lamp=9V. This is at the point where current =0.3A. Current in the same in series btw.
11. (Original post by pureandmodest)
http://www.edexcel.com/migrationdocu...e_20110117.pdf
question 2) and 5)
i'm so bad at anything to do with circuits so help would be much appreciated!
Q2:
Let's find the total circuit resistance and since we know emf, we work out current in circuit. Then

For parallel combination,
1/R=1/200+1/200
R=100kohms

Total circuit resistance=100+200
=300kohms

Let's work current in circuit, which is also current through parallel combination.
12=I X 300X10^3
I=4X10^-5

For parallel combination,
V=(4X10^-5) X (100X10^3)
=4V
12. Which experiments could come up? are there any hat we might be asked to describe?

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13. (Original post by Branny101)
Guys,
Do we need to know De Broglie's equation? As that involves momentum and that isn't part of the syllabus

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De Broglie's wavelength?
14. (Original post by pureandmodest)
http://www.edexcel.com/migrationdocu...e_20110117.pdf
question 2) and 5)
i'm so bad at anything to do with circuits so help would be much appreciated!
Q5:
N stays the same as its resistance is constant and current is constant, so by P=I^2R, brightness is constant.

Not sure with L
15. (Original post by krisshP)
Q2:
Let's find the total circuit resistance and since we know emf, we work out current in circuit. Then

For parallel combination,
1/R=1/200+1/200
R=100kohms

Total circuit resistance=100+200
=300kohms

Let's work current in circuit, which is also current through parallel combination.
12=I X 300X10^3
I=4X10^-5

For parallel combination,
V=(4X10^-5) X (100X10^3)
=4V
ahh i seeeee, thankya very much:]
16. (Original post by sarah.102)
Hi can you please look at the two questions I just posted and see if you can help me with them
I'll try, where are they?
17. (Original post by krisshP)
Q5:
N stays the same as its resistance is constant and current is constant, so by P=I^2R, brightness is constant.

Not sure with L
must be a then
18. (Original post by ambbs)
Which experiments could come up? are there any hat we might be asked to describe?

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Measuring wire resistivity
19. (Original post by Sarahftw_)
De Broglie's wavelength?
Are you doing this exam? I thought you fortunately switched exam boards?
20. (Original post by krisshP)
I'll try, where are they?
Bit confused by what actually is emf and potential difference and the differences between them
also guys what does this syllabus statement mean
"investigate and explain how the potential along a uniform current-carrying wire
varies with the distance along it and how
this variation can be made use of in a
potential divider"

thanks in advance i appreciate it

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