Lets revise physicsA2 togather ultimate thread Watch

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sumitk87
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#101
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#101
(Original post by Mr Tom)
same... wish i hadn't buggered it in january can't do the ole wave-particle duality nonsense

still its all better than PHY6
So u took phy4 in january :eek: , lucky our school dont do january exams .
what did u get in the exam if u dont mind me askin and was it a hard paper?
I dont kno what to expect from the paper
any topics that came up alot in the jan paper? (Does anyone have that paper ?)
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lilbug
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#102
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#102
(Original post by bassman)
wat does it mean by de broglie wavelength?
is it that a particle travels the same shape as a wave (sinusodially) or the particle has a wavelength? bit confused as i aint revised unit 4 for a very long time
the de Broglie equation is used for the wave behaviour of sub-atomic particles like electrons.

the particle doesn't travel in a sinosoidal shape (cos it IS the shape), rather the particle, for eg. an electron in an atom, is trapped inside the atom like a stationary wave is trapped in a rope.

as particles can behave like waves...the greater the velocity of the particle, the shorter will be its wavelength.
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habosh
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#103
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#103
(Original post by lilbug)
the de Broglie equation is used for the wave behaviour of sub-atomic particles like electrons.

the particle doesn't travel in a sinosoidal shape (cos it IS the shape), rather the particle, for eg. an electron in an atom, is trapped inside the atom like a stationary wave is trapped in a rope.

as particles can behave like waves...the greater the velocity of the particle, the shorter will be its wavelength.
also the mass,so thats way we dont see the effect of a travelling ball
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SinghFello
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#104
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#104
(Original post by sumitk87)
So u took phy4 in january :eek: , lucky our school dont do january exams .
what did u get in the exam if u dont mind me askin and was it a hard paper?
I dont kno what to expect from the paper
any topics that came up alot in the jan paper? (Does anyone have that paper ?)
I did PHY4 back in January, and I messed up.
Looking back(I got the exam paper back), it wasnt a difficult paper at all. It was slightly confusing at the time, but if I was presented with the same paper now, I could handle it much better. Its amazing how much difference 4 months can make.

Here is one of the questions that I really messed up on. Its a 7 mark explaination question!!

You are provided with a double slit whose slip separation is known to be 0.20mm. Describe how you would use it to measure the wavelength of the light from a monochromatic source. Mention any step you would take to make the measurement as accurate as possible.

You should include a diagram of the experimental arrangement, and state a suitable value for any other important dimensions.

(I drew a screen, and the monochromatic source, with the double slits in front of it. And I labled the distance as 6m. I only got 1/2 marks on this part)

On the explaination, I wrote(copying from my answer book):
Move the source next to the slits, so light travels through both. At the slits the light will defract and produce two coherent sources. The light from each slit will superpose, and form an interference pattern. This pattern can be observed on the screen at a pattern of high intensity and low intensity strips. The high intensities correspond to the maximas, which from when the waves at that point construct, due to being in phase. The low intensities correspond to the minimas where the wave destruct, due to being in anti-phase. There will be a centre maxima on the screen where the light from each slit would have travelled the same distance. Adjacent to this would be subsequant maximas on either side.
Using a ruler, measuring the distance between 3 or more maximas from the centre, you can find the distance between two maximas, S.(total distance/no. of maximas). Repeat and Average. Since Landa=xs/D, the wavelength can be measuring the distance between the slits and screen for D, and measuring the distance between the centre of each slit for x.


I got 2/7 for this question!
Anyone else think I got screwed over?
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corkskrew
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#105
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#105
Screwed by the exam board definately.
Personally I would have used a spectrometer.
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habosh
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#106
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#106
(Original post by SinghFello)
I did PHY4 back in January, and I messed up.
Looking back(I got the exam paper back), it wasnt a difficult paper at all. It was slightly confusing at the time, but if I was presented with the same paper now, I could handle it much better. Its amazing how much difference 4 months can make.

Here is one of the questions that I really messed up on. Its a 7 mark explaination question!!

You are provided with a double slit whose slip separation is known to be 0.20mm. Describe how you would use it to measure the wavelength of the light from a monochromatic source. Mention any step you would take to make the measurement as accurate as possible.

You should include a diagram of the experimental arrangement, and state a suitable value for any other important dimensions.

(I drew a screen, and the monochromatic source, with the double slits in front of it. And I labled the distance as 6m. I only got 1/2 marks on this part)

On the explaination, I wrote(copying from my answer book):
Move the source next to the slits, so light travels through both. At the slits the light will defract and produce two coherent sources. The light from each slit will superpose, and form an interference pattern. This pattern can be observed on the screen at a pattern of high intensity and low intensity strips. The high intensities correspond to the maximas, which from when the waves at that point construct, due to being in phase. The low intensities correspond to the minimas where the wave destruct, due to being in anti-phase. There will be a centre maxima on the screen where the light from each slit would have travelled the same distance. Adjacent to this would be subsequant maximas on either side.
Using a ruler, measuring the distance between 3 or more maximas from the centre, you can find the distance between two maximas, S.(total distance/no. of maximas). Repeat and Average. Since Landa=xs/D, the wavelength can be measuring the distance between the slits and screen for D, and measuring the distance between the centre of each slit for x.


I got 2/7 for this question!
Anyone else think I got screwed over?
I don't know why did they gave you 2/7 on this question I mean apart from not drowing the patter produced and indicate what the source is ie laser,you almost wrote down everything
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bassman
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#107
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#107
(Original post by habosh)
I don't know why did they gave you 2/7 on this question I mean apart from not drowing the patter produced and indicate what the source is ie laser,you almost wrote down everything
i think its to do with who marks your paper. some are v strict and sum are leanient.

i thought i messed up completely i didnt answer loads of questions in unit4 2005 i was expecting around 50ish but i ended up with 70, whereas my friend who described all the questions got 50 something.
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habosh
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#108
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#108
(Original post by bassman)
i think its to do with who marks your paper. some are v strict and sum are leanient.

i thought i messed up completely i didnt answer loads of questions in unit4 2005 i was expecting around 50ish but i ended up with 70, whereas my friend who described all the questions got 50 something.
that is honestly cruel I think the mark scheme says exactly what the dude wrote down :confused: I guess maybe he means it's what he would write now and not 4 months ago maybe :confused:
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Bezza
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#109
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(Original post by SinghFello)
You are provided with a double slit whose slip separation is known to be 0.20mm. Describe how you would use it to measure the wavelength of the light from a monochromatic source. Mention any step you would take to make the measurement as accurate as possible.

You should include a diagram of the experimental arrangement, and state a suitable value for any other important dimensions.

(I drew a screen, and the monochromatic source, with the double slits in front of it. And I labled the distance as 6m. I only got 1/2 marks on this part)

On the explaination, I wrote(copying from my answer book):
Move the source next to the slits, so light travels through both. At the slits the light will defract and produce two coherent sources. The light from each slit will superpose, and form an interference pattern. This pattern can be observed on the screen at a pattern of high intensity and low intensity strips. The high intensities correspond to the maximas, which from when the waves at that point construct, due to being in phase. The low intensities correspond to the minimas where the wave destruct, due to being in anti-phase. There will be a centre maxima on the screen where the light from each slit would have travelled the same distance. Adjacent to this would be subsequant maximas on either side.
Using a ruler, measuring the distance between 3 or more maximas from the centre, you can find the distance between two maximas, S.(total distance/no. of maximas). Repeat and Average. Since Landa=xs/D, the wavelength can be measuring the distance between the slits and screen for D, and measuring the distance between the centre of each slit for x.

I got 2/7 for this question!
Anyone else think I got screwed over?
well there are a few things you've missed - in the diagram you need a single slit between the source and the double slits to produce a coherent source so that's why you dropped a mark there. You should probably talk about path difference and phase difference, and at the maximas of intensity, the waves from the slits have a path difference of n\lambda so they're in phase and constructively interfere, and at minima, the path difference is (2n+1)\lambda/2, they're anti-phase so destructively interfere (they might not have liked you just saying construct and destruct as the wave doesn't really make or destroy itself!). You also just said you'd get an interference pattern but didn't really describe that it was succesive lines of high and low intensity - you could maybe have drawn a picture. It also asked for any other dimensions - you need to say the slit width is on the scale of the wavelength of light. When it comes to measuring the fringe spacing, they might have wanted you to say you'd measure between the middles of the maxima or something.

Although 2/7 seems fairly harsh, you missed a few important points and they'll have had a markscheme which they have to follow
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sumitk87
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#110
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#110
If thats exactly what singhfello wrote in the exam and only got 2/7 , He got screwed and im gettn scared, cos that was quite a gd answer and yet only 2/7, scary
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habosh
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#111
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#111
Ok,here is the markscheme the final thingie
suitable source,laser,or filament lamp,light source,monochromatic source plus a single slit 2 marks

double slit plus screen,or a travelling microscope (unless laser used)
measure distance from slits to screen(or focus plane of microscope)
measure spacing between centres of bright and dark fringes
subtitute in lambda=xs/D
3marks

they ask for precautions I guess
so measure distance across several fringes and find avarage x or maximise D to give maximium x
1 mark

values of D
laser=1-10 m
filament lamp 1-2m
travelling microscope 0.1-2m

so I guess one mark for not writing precautions,and another half for not indicating the source.mmm ok lets say a mark so why did he lose the other 5 marks??? ok and another for not drowing the patter for example ...that gives him minimum 4/7 :confused:
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sumitk87
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#112
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#112
hey habosh do u have the jan05 phy paper?
have u got in on yr computer or somin, if so is it possible to send it to me or post it on TSR. Or have u got the atcual paper
Thanks
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habosh
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#113
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#113
I got the paper as a mock exam]
Edit:I cant find the paper anywhere at the momenti'm so messy and my room is upside down
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sumitk87
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#114
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#114
(Original post by habosh)
I got the paper as a mock exam]
Edit:I cant find the paper anywhere at the momenti'm so messy and my room is upside down
not to worry, can u remember what topics came up roughly and what were the hard topics in it?
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SinghFello
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#115
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#115
Its kind of annoying when they dont give out marks.(BTW, I did say the precautions).
4 extra marks take you up one grade!

I also didnt get marks for the following parts:
(Haboosh, can you give the answers for these, because I wasnt given the answer sheet)

The final part of Q4 - Determine the amplitude of each of the travelling wave. I put 5mm.

Q5 - The reason why the graph confirms that the frequancy is inversly propotional to wavelength. Still not sure about this one?
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habosh
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#116
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#116
no it's 2.5mm ,the amplitude of the antinode is the vector sum of the amplitudes of bothwaves so the amplitude of each spearate wave is 2.5 also as it's a stationary wave then the amplitude is equal..part 5 it's because the graph is a stright line of negative gradient you can find the gradient which is the constant of the relationship lambdaf
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habosh
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#117
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#117
(Original post by sumitk87)
not to worry, can u remember what topics came up roughly and what were the hard topics in it?
magnetism..electrical field hard one i guess unless you practiced for these types of questions you'd find it easy..two chagrges
+(3uC) X - (1uC)
and then the girve a relation and prove the electrical field at that point is equal to that relation ...arrghh..I'm sos orry I cant concentrate any more I feel my brain is going to exploade
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bassman
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#118
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#118
(Original post by SinghFello)
Its kind of annoying when they dont give out marks.(BTW, I did say the precautions).
4 extra marks take you up one grade!

I also didnt get marks for the following parts:
(Haboosh, can you give the answers for these, because I wasnt given the answer sheet)

The final part of Q4 - Determine the amplitude of each of the travelling wave. I put 5mm.

Q5 - The reason why the graph confirms that the frequancy is inversly propotional to wavelength. Still not sure about this one?
the stationary wave is the result of the two waves superposing hence the amplitude of the single wave is half.

the graph was a log graph and straight line with negative gradient hence it was inversely proportional.

if u tell me the equation i can explain it to u
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haz136
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#119
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Hey, doin Edexcel A2 physics and just discovered this wonderful thread. Did a few of the questions but I'm struggling on a lot of Unit 4 stuff. Just been brwosing through a few unit4 papers and got stuck on a few. Was wonderin if some ppl could help me out:

1) Basically there was a question on equipment to produce a stationary wave using a signal generator. Then it says:
How is this phenomenon used to describe the behaviour of the electron in a hydrogen atom?

2) A student observes LED from a distance of 0.20m. The pupil of her eye has a diameter of 6.0mm. Calculate the number of photons which enter her eye per second.
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mackin boi
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#120
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#120
(Original post by haz136)
Hey, doin Edexcel A2 physics and just discovered this wonderful thread. Did a few of the questions but I'm struggling on a lot of Unit 4 stuff. Just been brwosing through a few unit4 papers and got stuck on a few. Was wonderin if some ppl could help me out:

1) Basically there was a question on equipment to produce a stationary wave using a signal generator. Then it says:
How is this phenomenon used to describe the behaviour of the electron in a hydrogen atom?

2) A student observes LED from a distance of 0.20m. The pupil of her eye has a diameter of 6.0mm. Calculate the number of photons which enter her eye per second.
1) An electron is described as oving on or in a stationary wave and so it does not loose any energy and spiral into the nucleus. It makes sence to an extent

2) is that all the info ure given??
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