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 Branny101)

Posted from TSR Mobile
Do you not understand how I explained it?
2. Anyone with Examiner's report for Jan 13 please? Urgent
3. (Original post by Tomupcraft)
Do you mean out of phase or 180 degrees out of phase? out of phase can be anything that is not in phase with a point, wheres a point in anti phase must be 180 degrees out of phase.
I meant 180 out of phase
4. (Original post by Tomupcraft)
Do you not understand how I explained it?
Sorry I just saw your reply, but doesn't frequency remain constant ?

Posted from TSR Mobile
5. (Original post by Branny101)
Sorry I just saw your reply, but doesn't frequency remain constant ?

Posted from TSR Mobile
Yes, If blue light goes from air into water its frequency will remain constant but its speed will decrease and so will its wavelength as when you draw diagrams the waves get closer together.

I wouldn't worry why shorter wavelengths refract more, just know that shorter wavelengths refract greater than larger wavelengths and therefore blue refracts more than red. So when you draw a diagram with a red and blue ray, the blue ray must refract closer to the normal.
6. (Original post by Tomupcraft)
One time period is between adjacent compressions. If the wave had traveled T the positions would basically look the same, the particles would have just moved up the line. However as 3/4T has passed then the compressions must be 3/4 along the line between two compressions.

If that does not make sense I will try to explain further.
Hi, is there any chance you could explain further, the bits that I don't understand is, if one wavelength (distance from 2 adjacent compressions ) is the time period as the time period = the amount of time taken for one complete oscillation, then how do we know where the particles would be at t +3/4T, I find it really confusing? Thanks
7. (Original post by alygirl)
I meant 180 out of phase
If you draw a diagram of a sine wave and label the axis 0, pi/2, pi, 3pi/2 and 2pi

Take the point 0, the point in phase with that is 2pi as it is a full wavelength ahead. Waves that are in phase are whole number of wavelengths ahead.

However the point at pi is not in phase with 0 as it is half a wavelength ahead, therefore it is out of phase. And because it is half a wavelength ahead this means it is in antiphase. Whenever two points are half a wavelength apart they are in antiphase.
8. (Original post by LegendX)
Hi, is there any chance you could explain further, the bits that I don't understand is, if one wavelength (distance from 2 adjacent compressions ) is the time period as the time period = the amount of time taken for one complete oscillation, then how do we know where the particles would be at t +3/4T, I find it really confusing? Thanks
The wave travels at a constant speed. So if we take the first compression, in one time period that compression will be in the same position as the second compression. As it travels at a constant speed if half a time period had passed then the first compression must now be half way between its original position and the original position of the second position.

If a tenth of a time period had passed then it would have been a tenth of the way along. Therefore if 3/4T has passed it must be three quarters between the original compression's.
9. (Original post by Tomupcraft)
If you draw a diagram of a sine wave and label the axis 0, pi/2, pi, 3pi/2 and 2pi

Take the point 0, the point in phase with that is 2pi as it is a full wavelength ahead. Waves that are in phase are whole number of wavelengths ahead.

However the point at pi is not in phase with 0 as it is half a wavelength ahead, therefore it is out of phase. And because it is half a wavelength ahead this means it is in antiphase. Whenever two points are half a wavelength apart they are in antiphase.
Thank youuuus , how is internal resistance measured?

Posted from TSR Mobile
10. Anyone please tell me how to do this?
Attached Images

11. (Original post by AT95)
Anyone please tell me how to do this?
I did that a couple pages back

(Original post by CharlieTT)
This is a combination of resistance in parallel and potential dividers equation.

1/R1=1/R.1 + 1/R.2
=1/6000Ohms +1/6000Ohms
=1/3000Ohms
R1=3 kiloOhms

Vout=Vin x R2/(R1+R2)
=12V x 6000Ohms/9000Ohms
=2/3 x 12V
=8V
12. (Original post by Tomupcraft)
If you draw a diagram of a sine wave and label the axis 0, pi/2, pi, 3pi/2 and 2pi

Take the point 0, the point in phase with that is 2pi as it is a full wavelength ahead. Waves that are in phase are whole number of wavelengths ahead.

However the point at pi is not in phase with 0 as it is half a wavelength ahead, therefore it is out of phase. And because it is half a wavelength ahead this means it is in antiphase. Whenever two points are half a wavelength apart they are in antiphase.
That makes sense. Sorry to bother you again, but please if you get a chance can you help me on Jan 2009 qu 13 b?
13. (Original post by Branny101)
Thank young, how is internal resistance measured?

Posted from TSR Mobile
If we take a solar cell as an example.
Have the solar cell in series with an ammeter and a variable resistor. Have a voltmeter in parallel with the solar cell.
Vary the resistance and record current and voltage.

as V = E - Ir rearrange to form V = -rI + E it is in the form y=mx+c
V on y axis
I on x axis
therefore E will be y intercept
so internal resistance, r will be the gradient.
14. (Original post by alygirl)
That makes sense. Sorry to bother you again, but please if you get a chance can you help me on Jan 2009 qu 13 b?
Current is split, if 30mA goes in then the current in both wires must = 30mA.
20mA in one wire so 10mA in the other wire so I1 = 10mA
15mA leave the first wire so 5mA must be remaining therefor I2 is 5mA
as current is conserved and 30mA went in, 30mA must also leave therefore I3 must be 30mA.
15. (Original post by Tomupcraft)
If we take a solar cell as an example.
Have the solar cell in series with an ammeter and a variable resistor. Have a voltmeter in parallel with the solar cell.
Vary the resistance and record current and voltage.

as V = E - Ir rearrange to form V = -rI + E it is in the form y=mx+c
V on y axis
I on x axis
therefore E will be y intercept
so internal resistance, r will be the gradient.
Thank you XD, what other experiments other than resistivity do we need to be able to understand and apply?

Posted from TSR Mobile
16. (Original post by Branny101)
Thank you XD, what other experiments other than resistivity do we need to be able to understand and apply?

Posted from TSR Mobile
Standing waves
Polarimetry
Finding resistivity of a metal

They are the main ones, I cannot remember any others off the top of my head.
17. (Original post by Tomupcraft)
Standing waves
Polarimetry
Finding resistivity of a metal

They are the main ones, I cannot remember any others off the top of my head.
The standing waves is just a tube with lycopodium powder right?

Posted from TSR Mobile
18. (Original post by Branny101)
The standing waves is just a tube with lycopodium powder right?

Posted from TSR Mobile
You mean Kundts tube? theres also the one with string attached to a mass hanging over a pulley.
19. (Original post by Tomupcraft)
You mean Kundts tube? theres also the one with string attached to a mass hanging over a pulley.
O__o... Let's stick with the glass tube ahaa

EDIT: I just realised the experiment you meant

Posted from TSR Mobile
20. Can someone please tell me the equation to calculate path difference from phase difference? And the equations derived from the doppler effect, asap would be awesome

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

Struggling to get going with your revision?

Get going with the all day revision thread

Uni strikes! How do they affect you?

Discussions on TSR

• Latest
Poll
Useful resources
Discussions on TSR

• Latest

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