The Physics PHYA2 thread! 5th June 2013

Was just looking on the January 2013 thread for this exam, just to see if there was any useful materials posted, someone posted some good last minute notes on the breakdown of each topic which was good, enjoy:

Mechanics:
1. The calculations are really easy IMO, just use SUVAT for most calculations :smile:

2. You need to be able to understand the graphs, which is pretty much common sense.
3. Know about Newton's laws, F=ma, every force has an equal an opposite force acting on it when the object is in equilibrium
4. Conservation of energy - really easy, basically max p.e. and min k.e. at top and max k.e. and min p.e. at the bottom. Why isn't all p.e. converted into k.e. when something is dropped in real life? because of energy being transferred to heat energy because of air resistance/ friction etc.
5. Definition and principle of a moment:
Definition = force x perpendicular distance from the pivot
Principle = sum of anticlockwise moment + sum of clockwise moment = 0
Think that's it really for mech...

Materials:
1. The practicals: obviously this depends on the practical that you are given but it's pretty much a summary of what you know and most of them award marks for the same things. One or two mentions for all the following should ensure at the very least half the marks. Reliability, Accuracy (like in fringe spacing, you would say increase D, perform in dark room, etc) maybe one for safety (like wear LASER goggles when using a laser, warn people not to look directly into the laser) Whenever you mention a measurement don't forget to mention a measuring instrument (vernier calliper for springs, wires, etc. *not sure* micrometer for fringe spacing?*not sure*. Also, don't forget to mention a graph and a table (maybe it helps to draw out the table yourself in pencil in a little corner so you know all the things that you need to do). I think that should cover it really for practicals.
2.Know Hooke's law: F=k[delta]L up to the limit of proportionality NOT the elastic limit as the elastic limit may sometimes come before the limit of proportionality.
3. Don't forget when making calculations from the graph to remember that it's in standard form.

Waves:
Possibly the hardest part of the course IMO but nothing too drastic
1. Be aware of the different types of waves but don't go mental over it, it's very rare that they ask you about the different types like mechanical, seismic etc. and if it does come up it's likely to only be 1 mark. However do be aware of transverse and Longitudinal waves. Transverse have direction of vibration perpendicular to direction of motion, Longitudinal have direction of vibration paralell to direction of motion. Also, be aware that transverse waves can be polarised and all the stuff that comes with polarisation, how it happens, what it does, what happens if you rotate the 2nd filter 90/ 180 degrees.
2. Refractive index, snells law etc.
Ok so basically n1.sin(i)=n2.sin(r) when r= 90 i=critical angle
when i= critical angle the light ray refracts along the boundary,
when i>ic total internal reflection occurs (i=r)
when i more dense = slows down and bends towards the normal
more dense -> less dense is the opposite and remember to flip the refractive index equation i.e. 1/n = sin(r)/sin(i)
3. Optical fibres: Uses include can transport data more quickly, therefore greater broadband speed, uses in medicine etc.
Core is made as narrow as possible to reduce multipath dispersion as waves travel less distance, cladding is used to protect the core, to help cause total internal reflection by having a lower/ higher refractive index not sure which can't remember now but it can be worked out...
4. Stationary aves and the fundamental waves:
The formation of a stationary wave: a string clamped at each end produces two proggressive waves at each end with the same constant phase difference, frequency amplitude, wavelength, equal and opposite velocities and they superimpose at the centre.
Fundamental waves this is quite easy and usually a very small section, know for the first that wavelength=2xlength. Also, know how to calculate frequency which is bsically just the rearrangement of the wave speed equation
5. Diffraction: This is when light is shone through a number of slits and you get a diffraction pattern so this is d.sin(pheta)=n(lamder)
n is the order of the beam and be aware that max order occurs when pheta=90 deg and DON'T round up when giving the max order, if you get 2.8 then the max order is 2
d will usually be given as the number of slits per mm, therefore d= 1/(number of slits)x10^3
6. Two source intereference: This is mainly the use of w=(lamder)D/s
remember just like the previous equation you may have to use this equation in explanations to show certain things are proportional/ inversely proportional
Know about destructive and constructive intereference and how you get maxima/ minima
7. Monochromatic vs. White Light:
Monochromatic = single wavelength
Monochromatic gives a dark/ bright fringe pattern with the bright fringe beng the colour of the laser unlike in white light which has multiple wavelengths and has a central bright fringe with blue inner fringes (either side of the central maxima) then you have a rainbow(you don't have to mention the rainbow) then you have the red outer fringe

Posted from TSR Mobile

Reply 102

Someone help in how to do moment calculations, don't just seem to get them :frown:

Reply 103

SortYourLife

16

Original post by Jimmy20002012

Someone help in how to do moment calculations, don't just seem to get them :frown:

Anticlockwise moment = clockwise moment for a system in equilibrium.

Moment = force * perpendicular distance to line of action (given on formula sheet)

Tbh, I *think* on this one, all the forces tend to be perpendicular, however I could be wrong and you may need to use sin or cos to find the perpendicular force

So wherever your pivot is, look at EVERY force acting on it, and follow a circle round one way. Assuming you have all your forces labelled, take into account every arrow that points in the same direction your circle is going, then an equals sign, then the same again with the other way round

That probably makes no sense and is probably better explained with an example, but i feel it is too late for me to be doing that now :tongue:

but if you would like an example I would be happy to do one :smile:

Reply 104

Original post by SortYourLife

Anticlockwise moment = clockwise moment for a system in equilibrium.

Moment = force * perpendicular distance to line of action (given on formula sheet)

Tbh, I *think* on this one, all the forces tend to be perpendicular, however I could be wrong and you may need to use sin or cos to find the perpendicular force

So wherever your pivot is, look at EVERY force acting on it, and follow a circle round one way. Assuming you have all your forces labelled, take into account every arrow that points in the same direction your circle is going, then an equals sign, then the same again with the other way round

That probably makes no sense and is probably better explained with an example, but i feel it is too late for me to be doing that now :tongue:

but if you would like an example I would be happy to do one :smile:

That sort of helped, how about a question like this:

http://filestore.aqa.org.uk/subjects/AQA-PHYA2-W-QP-JUN10.PDF

1c and 1d?

Posted from TSR Mobile

Reply 105

SortYourLife

16

Original post by Jimmy20002012

That sort of helped, how about a question like this:

http://filestore.aqa.org.uk/subjects/AQA-PHYA2-W-QP-JUN10.PDF

1c and 1d?

Posted from TSR Mobile

i know you didnt ask for 1b, but thought id include it as it has moments :smile:

hope i've helped!

Reply 106

Original post by SortYourLife

i know you didnt ask for 1b, but thought id include it as it has moments :smile:

hope i've helped!

I know it late :smile:

Think you might have done the first question wrong, it says find the moment of the bikers weight so it would be Moment= f x d= 780 x 0.35 = 273Nm.

For the second part, just few questions why do you ignore force Y and what do you mean by the furthest right?

Think you have made me sort of understand moments now, thanks soo much :smile:

Reply 107

SortYourLife

16

Original post by Jimmy20002012

I know it late :smile:

Think you might have done the first question wrong, it says find the moment of the bikers weight so it would be Moment= f x d= 780 x 0.35 = 273Nm.

For the second part, just few questions why do you ignore force Y and what do you mean by the furthest right?

Think you have made me sort of understand moments now, thanks soo much :smile:

Ah yeah I did! Sorry!

You ignore force Y as you're taking moments about point B, force Y is on point B, therefore your distance from the pivot is 0, giving you a moment of 0 (as 0* anything = 0) and so can be ignored

I just meant you're pivots at the end, so it ends up being up= down, as when some the pivots in the middle so like if you had an upwards force on each side of the pivot, one would be clockwise and one would be anticlockwise

And no worries, I hope I've helped aha!

Posted from TSR Mobile

Reply 108

Original post by SortYourLife

Ah yeah I did! Sorry!

You ignore force Y as you're taking moments about point B, force Y is on point B, therefore your distance from the pivot is 0, giving you a moment of 0 (as 0* anything = 0) and so can be ignored

I just meant you're pivots at the end, so it ends up being up= down, as when some the pivots in the middle so like if you had an upwards force on each side of the pivot, one would be clockwise and one would be anticlockwise

And no worries, I hope I've helped aha!

Posted from TSR Mobile

Thanks soo much, I actually get and can do moment calculations now, thanks again :biggrin:

Reply 109

UnknownGuy

2

What's the six marker predicted on?

Sent from my GT-I9100 using Tapatalk 4 Beta

Reply 110

Original post by UnknownGuy

What's the six marker predicted on?

Sent from my GT-I9100 using Tapatalk 4 Beta

Hopefully it's something like young modulus, but they may ask something to do with mechanics :smile: