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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 StUdEnTIGCSE)
Well if you ever want to define a physical quantity you can form an equation and make the denominator equal to one. (If you want to define a unit then make both the numerator and denominator one)

So voltage is energy transferred per unit charge or per coulomb of charge. (And one volt is one joule transferred per coulomb charge).

This does not specify if it is inputting or outputting electrical energy. So we have emf.

Emf of a battery or cell is the total work done by the cell against both the internal and external circuits per coulomb of charge that passes through it. It is different to the terminal pd learnt at GCSE which does not recognise internal resistance so terminal PD is the work done by the cell in the external circuit only.

In other words emf is the total electrical energy provided to each coulomb of charge by a power supple. This energy is then used to do work in the internal circuit (against internal resistance) and in the external resistance. Lost volts us the work done in the internal circuit against internal resistance.

So emf=lost volt+terminal pd
Terminal PD= emf - lost volt

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(Original post by sarah.102)
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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2. (Original post by krisshP)
Measuring wire resistivity
Thanks :-) is that it? I can't think of any others but seeing as there wasn't an experiment q in unit 1 I want to be prepared in case they throw one in for unit 2!

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3. (Original post by sarah.102)
[COLOR=#505050][FONT=Arial]Bit confused by what actually is emf and potential difference and the differences between them
Emf is energy transferred TO a charge as it passes through the power supply
Pd is the energy transferred FROM a charge to components in the external circuit

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4. (Original post by sarah.102)
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
Well the syllabus statement is very important but takes a great deal of time to explain.
Hope this helps
http://www.s-cool.co.uk/a-level/phys...ntial-dividers

The two things that you must remember are:

Firstly

When the resistivity/material is the same as well as the cross sectional area resistance is directly proportional to length.

Secondly

Using V=IR when current is the same voltage is directly proportional to the resistance, and voltage is the same as in parallel.

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5. (Original post by StUdEnTIGCSE)
Well the syllabus statement is very important but takes a great deal of time to explain.
Hope this helps
http://www.s-cool.co.uk/a-level/phys...ntial-dividers

The two things that you must remember are:

Firstly

When the resistivity/material is the same as well as the cross sectional area resistance is directly proportional to length.

Secondly

Using V=IR when current is the same voltage is directly proportional to the resistance, and voltage is the same as in parallel.

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Will potential divider questions ever involve emf also (I.e. if internal resistance is involved, what do I use as V in, the emf?)

Thanks
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6. (Original post by pureandmodest)
must be a then
What about L I don't get it.
7. (Original post by sarah.102)
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
EMF is the amount of energy supplied to a unit charge coulomb.

PD is energy transferred from a unit charge coulomb to the circuit between two points.

The syllabus is just talking about potential dividers there.
8. (Original post by krisshP)
What about L I don't get it.
aw thats cute
and neither do i, but it would have to be a if N does stay the same?:c
9. Can somebody please explain q5 in Jan 2011. I know why N is same, but not L.
10. (Original post by krisshP)
Can somebody please explain q5 in Jan 2011. I know why N is same, but not L.
N isn't the same. The answer is D.

I will have a go at it.
Basically if M goes off the resistance in the circuit would increase, because of the parallel combination. Linking it to I=V/R if R increases then I, current, would decrease in the circuit. Linking this to power, P=IV, for bulb L there would be an increase in power, meaning an increase in brightness because of the increase incurrent. For N I am not too sure how the brightness would decrease.
Not 100% on this, so If anyone knows better please add and correct me if I was wrong.
11. (Original post by B-Stacks)
N isn't the same. The answer is D.

I will have a go at it.
Basically if M goes off the resistance in the circuit would increase, because of the parallel combination. Linking it to I=V/R if R increases then I, current, would decrease in the circuit. Linking this to power, P=IV, for bulb L there would be an increase in power, meaning an increase in brightness because of the increase incurrent. For N I am not too sure how the brightness would decrease.
Not 100% on this, so If anyone knows better please add and correct me if I was wrong.
If M goes off, do we say that resistance of M decreases, or do we say that there's no parallel combination and just a series of 2 lamps?
12. (Original post by krisshP)
Are you doing this exam? I thought you fortunately switched exam boards?
Yeah, I am

Idk what the science department are playing at tbh
13. Anyone know how I would work out the reading on the voltmeter?
Attached Images

14. (Original post by Sarahftw_)
De Broglie's wavelength?
Something like that, yeah!

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15. (Original post by LegendX)
Anyone know how I would work out the reading on the voltmeter?
Yeah i want to know as well how to do (a) and (b).
16. (Original post by Branny101)
Something like that, yeah!

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That's in A2.

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17. Exam time and date fellas?
18. Jan 2012, q7. The answer is A but I don't get why! Thanks in advance
19. (Original post by stealth_writer)
Exam time and date fellas?
Wed 5th June, 9am
20. (Original post by wirralriddler)
P.d across branches in parallel with the power supply are always equal to the voltage across the power supply I think. So the answer would just be 15v?
That's what I thought until I saw the R1 resistor and I realised it couldnt be.

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