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# The Physics PHYA2 thread! 5th June 2013 watch

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1. (Original post by Nav_Mallhi)
I feel pretty screwed for physics as well, had bio on Monday and Chem today. And I'm seeing that you had the pleasure of sitting the chem paper today as well?

I'm looking for a list with all the experiments as well, I think the ones we need to know are just: Hookes law, Youngs Modulus, Diffraction (single and double slit)

(Original post by pushkin_)
Does anybody have notes going through everything we need to know?
Yup, I'm in panic, haven't done any solid revision for physics, just past papers and I would be VERYYYYYYYYYYYYY thankful If somebody could share with their revision notes.

p.s. have anybody posted all unit 2 experiments in this thread ? pleaaase , somebody help, I feel so miserable in first place because of todays chemistry.

some one posted the experiments we need to know earlier in this thread so credits to them !!! (attachment)

and earlier on in this thread i made some key points (apologies to those who've seen it and think im taking up space).

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.

• 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 !!!!!
Attached Images
2. Experiments.pdf (308.7 KB, 316 views)
3. (Original post by CJG21)
Erm... too many words I don't get there.

I still don't understand TIR when it's not in an optical fibre.

I'm going to fail this. I can't do anything.
Do not worry! Just focus as much as you can for now. Here is a lovely picture for you. Consider a horizontal line to be the water surface. The diagram shows the rays are coming out from the water into the air. So, the dotted line is the normal. Angle between the normal and the incident ray (incident ray which is coming out of the water) is called the incident angle. Is that clear now?
4. (Original post by masryboy94)
some one posted the experiments we need to know earlier in this thread so credits to them !!! (attachment)

and earlier on in this thread i made some key points (apologies to those who've seen it and think im taking up space).

Hope it helps !!!!!
I seriously consider everyone take a look on the diffraction grating one, that sounds like a likely question they would ask. Thanks for this bro!
5. (Original post by StalkeR47)
Like this m8.
to my eyes that is showing a continuous spectrum
6. (Original post by masryboy94)
to my eyes that is showing a continuous spectrum
Each fringe is a continuous spectrum. But, each fringe showing a continuous spectrum is called maximum. The dark sides are minimum. Is that clear m8?
7. In the January 2012 paper question 1c, why does the speed/acceleration of the ship affect the horizontal force exerted by the cable on the ship?
8. (Original post by masryboy94)
to my eyes that is showing a continuous spectrum
Are we talking about double slit, or single ?

If it's double then there would be some interference
9. (Original post by Raimonduo)
I seriously consider everyone take a look on the diffraction grating one, that sounds like a likely question they would ask. Thanks for this bro!
no worries and yeh i agree with you on that one ... but i also think they might go into mechanics (about Ep and Ek) its comes up once (about the trampoline in june 09 and thats it, so something similar might come up
10. Has anyone done the Jan 2013 paper? If so, could someone possibly explain the very last question?

Thanks!
11. Can anyone help with June 2011 question 5d? i don't get it at all, its a optical fibre question
would be greatly appreciated
12. (Original post by masryboy94)
some one posted the experiments we need to know earlier in this thread so credits to them !!! (attachment)

and earlier on in this thread i made some key points (apologies to those who've seen it and think im taking up space).

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.

• 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 !!!!!

You are my savior ! Now I'll stop crying because of my chemistry and I'll start doing what I can with physics.
Thaanks again !
13. (Original post by StalkeR47)
Each fringe is a continuous spectrum. But, each fringe showing a continuous spectrum is called maximum. The dark sides are minimum. Is that clear m8?
yeh i guess so, thanks !!
14. (Original post by Claree)
In the January 2012 paper question 1c, why does the speed/acceleration of the ship affect the horizontal force exerted by the cable on the ship?
Yes but the ship has a constant velocity, so no acceleration.
15. (Original post by pushkin_)
You are my savior ! Now I'll stop crying because of my chemistry and I'll start doing what I can with physics.
Thaanks again !
haha aww dw, im happy to help how was you chem?
16. (Original post by masryboy94)
yeh i guess so, thanks !!
No probs!
17. 5d of June 2011?! I really don't understand...
18. (Original post by masryboy94)
yeppp
Thank you!
19. Can someone explain Jan 2013 Question 7e, why we have to include 'Maximum', and also June 2009, Question 3b, and also 3d on Jan 11, as I thought the intensity would increase as technically speaking the effect of decreasing the slit would decrease D
20. can i just stress that for SINGLE SLIT DIFFRACTION the intensity on an intensity graph will reduce. whilst for a DOUBLE SLIT DIFFRACTION the intensity on an intensity graph will stay the same or similar to the maximum central. not totally sure why, but theres a good chance it could come up and you need to realise the difference between the two !!!!
21. (Original post by StalkeR47)
Yes but the ship has a constant velocity, so no acceleration.
But the mark scheme says that if you were to alter the velocity or acceleration the horizontal force would be affected. What I don't understand is how the ship's speed changing could affect the horizontal force.

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