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# The Physics PHYA2 thread! 5th June 2013 Watch

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1. question 2a in june 2010 is ****ing retarded

the answer in the mark scheme doesn't even match up with whats asked

2. (Original post by Jack93o)
question 2a in june 2010 is ****ing retarded

the answer in the mark scheme doesn't even match up with whats asked
The one about freefall? I agree -.-

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3. (Original post by eilish1903)
Yes light of different wavelengths are diffracted by different amounts. For example red and blue light. They are diffracted by different amounts and produce fringe patterns. The fringe patterns produced are different due to the wavelengths.
U don't need to know why.
U just need to know that the longer the wavelength the greater the fringe patterns...

Any help at all??

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I was talking about refraction, not diffraction. They're not the same thing are they?

when you shine a red light at a glass block, does it have a different angle of refraction than say for example, blue light?

4. (Original post by fuzzybear)
For refraction, am I right in thinking that light of different wave lengths would be refracted by different amounts?

and if so, why?

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5. (Original post by x-Sophie-x)
The one about freefall? I agree -.-

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yeah, pissed me off

a few more things as well from this june 2010 paper...

for 5b, on the question paper, it only has 3 marks. But on the mark scheme, it shows 4 marks for that question

btw for question 3cii, does the graph have to have 'smooth' slopes (kind of like a cosine wave), or is it alright to just draw a straight 'W'shape?

the mark scheme is rather ambiguous on this
6. (Original post by fuzzybear)
I was talking about refraction, not diffraction. They're not the same thing are they?

when you shine a red light at a glass block, does it have a different angle of refraction than say for example, blue light?
No refraction is when the light travels from one medium to another.

I'm assuming you asked if wavelength effects the amount of refraction. Yes it does When white light goes through a glass or prism for example. The reason you get the funky rainbow spectrum is because each colour has a certain wave length and therefore is refracted at different angles.
7. (Original post by fuzzybear)
I was talking about refraction, not diffraction. They're not the same thing are they?

when you shine a red light at a glass block, does it have a different angle of refraction than say for example, blue light?
oooohhh!! they don't.
think of this. if you shine a white light through a prism, you get a rainbow. this is because the wavelengths are refracted by different amounts (red being the most and blue being the least.
8. (Original post by Jack93o)
yeah, pissed me off

a few more things as well from this june 2010 paper...

for 5b, on the question paper, it only has 3 marks. But on the mark scheme, it shows 4 marks for that question

btw for question 3cii, does the graph have to have 'smooth' slopes (kind of like a cosine wave), or is it alright to just draw a straight 'W'shape?

the mark scheme is rather ambiguous on this
Straight lines should do the trick, the mark scheme says reasonable shape.

(Original post by spleenharvester)
I'm hoping the coursework boundaries are low this year, I got 59/70 in the Jan exam but only 29/50 in the coursework, so I'm really gonna have to push it for this one
Coursework boundaries are never low, they're just a joke to be honest. An A is 48 UMS I think, but to get that much UMS you need very high marks. A friend of mine was on that borderline with about 40-42 marks.
9. Here are some key points i made for all of you for PHYA2 to bare in mind:

• Forces acting on an object in equilibrium form a closed loop (Vector triangle)
• Define moment: force x perpendicular distance, and is the turning effect of a force around a turning point.
• Principle of moment: For a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point.
• Torque = Force (Turning force) x perpendicular distance between them.
• gives the gradient on a curve to be velocity. and since is acceleration, therefore the stepper the curve the greater the acceleration.
• Newton's First Law: An object will stay at rest or in uniform velocity, unless a resultant foce acts on it.
• Newton's Second Law: Acceleration is proportional to the resultant foce acting on it at a certain mass. F=ma
• Newton's Third Law: When 2 objects interact, they exert an equal and opposite force on eachother.
• Free fall is when the only force acting on an object is gravity.
• For projectile motion: VERTICAL you use SUVAT, for HORIZONTAL you use and in both cases 't' is the same.
• When Friction force = Driving Force object stops accelerating and reaches its terminal velocity.
• Types of friction: Contact (Friction), Fluid (Drag, Air resistance, Fluid Resistance)
• Principle of conservation of energy: Energy cannot be created or destroyed, but can be transferred from one form to another.

• Hooke's Law: Extension is proportional to force given it is within the limit of proportionality.
• Experiment to investigate extension:

1) Object should be supported using a G-clamp
​2) Measure original length using a ruler
3) Masses should then be added in 100g intervals up to atleast
600g.
4) For each mass added, calculate new extension using (new
length - original length).
6) Repeat experiment 3 times taking an average result.
7) Plot a graph of force against extension to show results.

• Elastic and Plastic deformation: If elastic, material will return to original length. Elastic when material will not return to original length
• Young Modulus:
• Young's Experiment:

1) Set up experiment.
2) Add enough mass to straighten wire but not extend it.
3) measure original length using a ruler
4) Add in intervals of 100g of mass up to what it could withstand, and for each mass added read off the new length by using a travelling microscope or vernier calliper.
5)calculate extensions by using (new length - original length)
6) Measure cross sectional area using , to obtain D, you would used a micrometer and measure at different positions on the wire and take an average reading.
7) Repeat experiment 3 times
8) plot a graph of stress against strain and gradient will give young modulus or Young Modulus = .

• Waves are vibrations, they only carry and transfer energy.
• 4 things a wave can do:

1) Reflect - Wave bounces back when hitting a boundary.
2) Refract - wave direction changes as it enters a medium
3) Diffract - wave spread out
4) Interfere - 2 waves co-join

• Phase difference: Amount by which one wave lags behind another wave.
• Transverse waves: Vibrations oscillating at right angles to the direction of travel (Electromagnetic waves, waves on rope, ripple of water ...etc)
• Longitudinal waves: Vibrations oscillating along direction of travel (sound)
• Application of polarisation: Glare reduction (polaroid sunglasses). Improving TV and radio signals by lining up the rods of the receiving aerial to the transmitting aerial.
• Optical fibres: light in optical fibres is used to transmit phone and cable TV signals. Light doesn't heat up fibre therefore little energy loss. No electrical interference. and it is a cheaper alternative.
• Signal loss (reduction in amplitude) in optical fibres are caused by energy lost through absorption and scattering.
• Signal broadening is caused by multi-path dispersion which is when the signal travels straight down the middle and arrives earlier than those undergoing T.I.R.
• Principle of Superposition: When 2 or more waves cross, the resultant displacement equals the vector sum of the individual displacement.
• Constructive interference: when displacement combine to make an even bigger one (e.g. crest plus crest)
• Destructive interference: when negative and positive displacement combine to cancel out (e.g. crest plus trough)
• Stationary or standing wave: is the superposition of two progressive waves with the same frequency and amplitude travelling in opposite directions towards each other. this is when you get fundamental frequency which is . if you double the fundamental frequency you get the second harmonic (first overtone). Triple the fundamental you get third harmonic (second overtone) and so on ...
• Fundamental frequency depends on the length, mass and tension of a spring.

1) if length increases, frequency decreases
2) if mass increases, frequency decreases
3) if tension increases, frequency increases

• Application of stationary waves: Microwaves, sound waves.
• you get greatest diffraction if the slit size is equal to
• Laser is monochromatic (has a single wavelength) and coherent (same frequency and constant phase difference).
• laser beams are powerful and can cause damage to eyesight, this can be prevented by wearing safety laser goggles or removing any reflective surfaces.
• Path Difference: how much further a wave has travelled than the other wave.
• When you get constructive interference, at your first order(s) [bright fringes] your path difference is where is an integer this also means that the phase difference is a multiple of .

• where you get [dark fringes] between say zero and the first order or first and second order, the path difference is where the phase difference is a multiple of (for it to be perfectly out of phase).
• non - coherent light such as white light will have wider maxima containing different colours with central white fringe. light is continuous range of frequencies
• Young's double slit experiment: . w is fringe spacing. is wavelength, s is spacing between slits, and D is distance from slits to screen.
• Diffraction grating: They have more slits causing bright bands to be brighter and narrower and dark fringes to be even darker. monochromatic light is used causing interference patterns to be sharper and more accurate of a measurement.

Hope it helps !!!!!
10. Can anyone explain this?

http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF
http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF

Question 7c - the mark scheme specifies that the answer is to do with polarisation

But page 179 in the Nelson Thornes textbook has the exact same thing about TV signals/aerials, but the explanation to do with diffraction instead. I don't get why it's different?
11. for a diffraction grating (and a double slit), is slit spacing measured from centre of the slits?

also for a double slit, do you need to know about the difference in width between bright and dark fringes? like for example, what would cause bright fringes to be wider than the dark fringes that separates them and vice-versa?
12. (Original post by House MD)
Can anyone explain this?

http://filestore.aqa.org.uk/subjects...2-QP-JUN12.PDF
http://filestore.aqa.org.uk/subjects...W-MS-JUN12.PDF

Question 7c - the mark scheme specifies that the answer is to do with polarisation

But page 179 in the Nelson Thornes textbook has the exact same thing about TV signals/aerials, but the explanation to do with diffraction instead. I don't get why it's different?
Page 175 in the small green box is where it explains it. The diffraction bit is either specifically for Satellite dishes (maybe for a future question) or the book just likes confusing us.
13. Can someone look at Q6a.ii
They ask for the phase relationship between X and Z. Mark scheme says in phase, 2pi, zero degrees. Is it just me being picky or is the diagram a bit off? X isn't at the peak of the wave, it's slightly past it.

Edit: June 12
14. (Original post by NedStark)
Can someone look at Q6a.ii
They ask for the phase relationship between X and Z. Mark scheme says in phase, 2pi, zero degrees. Is it just me being picky or is the diagram a bit off? X isn't at the peak of the wave, it's slightly past it.
which paper?
15. (Original post by masryboy94)
which paper?
June 12
16. (Original post by NedStark)
June 12
they are in phase because they move up and down at the same time. Phase difference for stationary waves isn't linked to the distance between them instead its the number of nodes
17. (Original post by Goods)
they are in phase because they move up and down at the same time. Phase difference for stationary waves isn't linked to the distance between them instead its the number of nodes
In Jan 13 1d:
"Explain, with reference to energy, why the velocity of the diver is independent of his mass if air resistance is insignificant."

The markscheme says:
(all G)PE (lost) is transferred to KE
no (GP)E transferred to ‘heat’ / ‘thermal’ / internal energy

How does that answer the question?
18. (Original post by NedStark)
June 12
its hard to explain, but if you look at this video from 23.30 https://www.youtube.com/watch?v=jSLw01C9Pv8 the concept that he shows is what they mean by this question, its a badly worded question but yh like the post above me said its not the phase difference but there actual movement hope that clears it up
19. (Original post by NedStark)
In Jan 13 1d:
"Explain, with reference to energy, why the velocity of the diver is independent of his mass if air resistance is insignificant."

The markscheme says:
(all G)PE (lost) is transferred to KE
no (GP)E transferred to ‘heat’ / ‘thermal’ / internal energy

How does that answer the question?
Hi! I was also stuck on this question. The question is relatively easy but the fact that no GPE is converted to KE is confusing. I think little GPE is converted into KE and rest is wasted as heat, sound due to friction and air resistance. EDIT: Sorry, I thought it was Q2) For 1d) All GPE is converted to KE because there is no friction.
20. (Original post by NedStark)
In Jan 13 1d:
"Explain, with reference to energy, why the velocity of the diver is independent of his mass if air resistance is insignificant."

The markscheme says:
(all G)PE (lost) is transferred to KE
no (GP)E transferred to ‘heat’ / ‘thermal’ / internal energy

How does that answer the question?
(Original post by StalkeR47)
Hi! I was also stuck on this question. The question is relatively easy but the fact that no GPE is converted to KE is confusing. I think little GPE is converted into KE and rest is wasted as heat, sound due to friction and air resistance. EDIT: Sorry, I thought it was Q2) For 1d) All GPE is converted to KE because there is no friction.
mgh = 1/2 mv^2

m cancel out

EDIT: It is a pretty stupid question.... but there's more friction for bigger masses. They've made it negligible in this question.

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