You are Here: Home >< Physics

# 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 pureandmodest)
could someone explain the very last question on the june09 paper?
http://www.edexcel.com/migrationdocu...e_20090521.pdf
thankyou..
The answer on the mark scheme is pretty self explanatory... If you are talking about 21)d
2. (Original post by B-Stacks)
The answer on the mark scheme is pretty self explanatory... If you are talking about 21)d
(Original post by Branny101)
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.

Posted from TSR Mobile
Could you explain paleeze, mate?

Posted from TSR Mobile
3. (Original post by B-Stacks)
The answer on the mark scheme is pretty self explanatory... If you are talking about 21)d
i don't get it though
it says something about it increasing in length or something
but it doesn't.. the length is the same._.
sorry, i'm really stupid something. i'd appreciate it if someone spelt it out to me :c
4. (Original post by pureandmodest)
i don't get it though
it says something about it increasing in length or something
but it doesn't.. the length is the same._.
sorry, i'm really stupid something. i'd appreciate it if someone spelt it out to me :c
So you have a long wire. If you put it in a zigzag shape this long wire will take up a lot less space as its all closely packed together. If you increase the length of this wire there still won't be that much of a difference to the space taken up. Using the equation R=pl/A if there is an increase in l, length, we know there would be a greater increase in r, resistance.
5. (Original post by Branny101)
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.

Posted from TSR Mobile
What do you mean? Are you sure it's 20)b.i ?
6. (Original post by B-Stacks)
What do you mean? Are you sure it's 20)b.i ?
Yeaah cause it says ( in the mark scheme ) times the wavelength by two, but isn't that only in standing waves?

Posted from TSR Mobile
7. (Original post by Branny101)
Yeaah cause it says ( in the mark scheme ) times the wavelength by two, but isn't that only in standing waves?

Posted from TSR Mobile
You times the wavelength by 2 because the question says the distance between two adjacent maxima. In a standing wave you know that two adjacent maxima would be the distance between two antinodes. Draw a quick sketch if you need and you will realise that this distance 0.05m is half a wavelength. Which means you'd need to times it by 2.

Also it is a standing wave... Sound waves can also be stationary.

8. (Original post by B-Stacks)
You times the wavelength by 2 because the question says the distance between two adjacent maxima. In a standing wave you know that two adjacent maxima would be the distance between two antinodes. Draw a quick sketch if you need and you will realise that this distance 0.05m is half a wavelength. Which means you'd need to times it by 2.

Also it is a standing wave... Sound waves can also be stationary.

Ahhhh okay the first bit makes sense, but the second part, I thought they only formed in tubes?

Posted from TSR Mobile
9. (Original post by Branny101)
Ahhhh okay the first bit makes sense, but the second part, I thought they only formed in tubes?

Posted from TSR Mobile
Not too sure, but looking at this question I guess they don't have to be in tubes.
10. (Original post by B-Stacks)
Not too sure, but looking at this question I guess they don't have to be in tubes.
Okay, thanks

Posted from TSR Mobile
11. What core practicals do we have to know, I know that resistivity came up in jan
12. (Original post by TheFuture001)

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
This was quite a mean question to give in unit 2 :/
basically in unit 5 you actually learn the equation you have to use:
L/4πd2
(i just used this equation since im retaking and have already covered unit 5)

so the question is a bit misleading by telling you to use "r" instead of "d" however in the scenario given, d is equal to r, so it doesn't matter;

"Assume that a distance r from the source the energy is spread over a total area 4πr2 "

so you just have to be very careful reading the question and see that they specify that distance happens to be equal to r.

I was wondering for ages how someone doing unit 2 would know how to work that out, then i finally noticed the sneaky r in the question
13. Hey, guys, when you have a question that says "show that blah blah is approximately equal to blah blah" , for the next question do you use the approximate answer given in the question before or the value you calculated?
14. (Original post by *mike)
Hey, guys, when you have a question that says "show that blah blah is approximately equal to blah blah" , for the next question do you use the approximate answer given in the question before or the value you calculated?
You can use either. The mark scheme always credits you for either.
15. So what are the predictions for tomorrows exam? I have a feeling string instruments might come up.
16. (Original post by B-Stacks)
You can use either. The mark scheme always credits you for either.
Thanks! I assume you get ft marks if you use your value calculated and it was wrong?
17. When asked to find the potential difference across a resistor in a potential divider circuit , can the potential divider formula be used to find the p.d.Normally 3 marks are given for this type of question.
Or else we have to go the long way of finding the current in the circuit and then finding the p.d. across resistor.

Posted from TSR Mobile
18. (Original post by *mike)
Thanks! I assume you get ft marks if you use your value calculated and it was wrong?
But if its a 'show that' its unlikely your value will be wrong, unless you had no idea how to get the answer. If that's the case just use the value 'show that' value for the next question.
19. (Original post by blacknightking)
When asked to find the potential difference across a resistor in a potential divider circuit , can the potential divider formula be used to find the p.d.Normally 3 marks are given for this type of question.
Or else we have to go the long way of finding the current in the circuit and then finding the p.d. across resistor.

Posted from TSR Mobile
Yes, if you know the the EMF and two Resistance values of the resistors.
20. Got a question from Jan 11 http://www.edexcel.com/migrationdocu...e_20110117.pdf

Its question 19 aii)

I thought that the minimum vertical distance would be half a wavelength (as that corresponds to 180 degrees and would be the smallest unit of distance possible for this much out of phase) however the mark scheme gives the answer as a quarter of the wavelength, really confusing me, any help much appreciated.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: December 18, 2013
Today on TSR

### Falling in love with him

But we haven't even met!

### Top study tips for over the Christmas holidays

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Useful resources

Can you help? Study help unanswered threadsStudy Help rules and posting guidelinesLaTex guide for writing equations on TSR

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.