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# OCR Physics A AS Forces+Motion/Electrons & Photons revision thread watch

1. Done this revision thread last year, though I'd bring it back if anyone needs help/revision notes.

ps: its also useful for all doing the synoptic paper, remember ANYTHING could come up

Forces and Motion (AS Module)

Kinematics

A Physical quantity with size only is called a scaler (energy,speed,length,distance)
A Physical quantity with size and direction is called a vector (Force,Velocity,accel)

V=S/t
Velocity is the displacement per unit time measured in ms^-1

The gradient of a distance time graph gives speed
The gradient of a displacement time graph gives velocity

.a = v – u/t acceleration is rate of change of velocity measured in ms^-2
gradient of velocity time graph gives acceleration
area under velocity time graph gives distance travelled

you should know how to derive the equations of motion

v=u+at, v^2=u^2+2as, s= (u+v/2) *t
these are just 3 of the equations, but you still need to know the other 2.

Dynamics

Newtons second law states that force is proportional to the rate of change of momentum. F=ma

Momentum is mass*velocity

Mass is the quantity of matter of a body.

The Newton is defined as the force needed to accelerate a mass of 1kg by 1ms^-2

Density is the mass per unit volume measured in Kgm^-3

Weight=mg where g=9.8i ms^-2

You need to know the effects of air resistance on motion. Eg initially no drag a=9.81, after a short while drag increases, there is a resultant force etc etc

Forces,work and power

Pressure= force per unit area measure in pa (pascals)

The moment of a force about a point is the product of the force F and the perpendicular distance of the force from the point x. you should also know how to show this in a sketch

Moments are measured in Nm.

OCR expect you to know the Principles of moments- if in equilibrium the clockwise moments equal the anticlockwise moments.

The centre of gravity is the point which the whole weight of the object seems to act.

Energy is the potential to do work, work is done when energy is TRANSFORMED from one form to another.

Work done is force *distance moved in direction of force

Potential energy = m*g* change in height P.E = mgh

Kinetic energy= 1/2mv^2

Work and energy are both measured in Joules (J)
1J is the work done when a force of 1N moves through a distance of 1m in the direction of the force.

Power is defined as the work done per unit time. P=W/t

Make sure you know how to derive P=Fv, this question is sometimes asked.

One watt is defined as one joule per second.

Deformation of solids

You need to know hookes law: the extension of a string is proportional to the force(F) acting on it.

The spring constant is the force per unit extension, on a graph of F against x you can find the spring constant by finding the gradient.

Stress is defined as force per unit area

Strain is defined as the extension per unit original length.

Youngs modulus= Tensile stress/tensile strain and has units Nm^-2 or Pa

You need to explain how the youngs modulus can be found. This is a very popular question. ie use vernier scale to measure extension etc etc

Car safety

Learn how seat belts, air bags, crumple zones are useful and make sure you talk about physical factors such as a crumple zone absorbs kinetic energy, don’t write it ‘softens the crash’.

Conditions which affect stopping/braking/thinking distance also need to be known things like tyre thread, weather conditions etc etc

Electrons and Photons (AS Module)

Electric Current

1C is the amount of charge which flows past a point when a current of 1 ampere flows for 1 second

Q=I*t or I=Q/t Current is the charge per unit time measured in Amps

V=W/Q potential difference is the work done per unit charge

You need to be able to define Ohms law: For a conductor at constant room temperature. The current in the conductor is proportional to the voltage across it.

Resitivity = Resitance*Cross sectional area/length
p=R*A/l

From this you should be able to rearrange for the other 3 formulas for R,l and A

Remember if A increases then resistance and resistivity decrease.

Power is the rate of transfer of energy and is measured in W (watts)

It can be found using P=W/t, P=IV, P=I^2R, P=V^2R

Energy = IVt which is power multiplied by time

You need to be able to define a volt. A joule per columb

D.C Circuits

If you have resisitors in series you add them, so Rt= R1+R2+R3……….

If you have resitors in parallel 1/Rt = 1/R1+1/R2+1/R3…………

e.m.f is defined as the work done on unit charge in driving it round a complete circuit

V=E-Ir

1J=1kgms^-2m

you need to know and recall Kirchoffs laws which are

1st: The sum of the currents flowing into any point in a circuit is equal to the sum of the currents flowing out of that point.

2nd: The sum of the e.m.f’s around any loop in a circuit is equal to the sum of the P.d’s around that loop.

Magnetic effects of current

You need to know how to sketch magnetic field patterns caused by current in a long straight wire, a flat circular coil and a long solenoid. ( I would be grateful if someone posted these patterns here)

Magnetic Field strength or Flux density is defined as the force per unit length per unit current measured in T (Tesla)

You need to be able to define the tesla which is the flux density needed to produce a force of one newton on a wire carrying a current of one amp at right angles to the magnetic field.

Make sure you know how to use flemings left hand rule to predict the direction of forces acting on two long, straight parallel current carrying conductors.

F=BIl with directions interpreted by flemings left hand rule.

Quantum Physics.

This topic is the most difficult in the specification, and will probably be the qualitative question in the exam.

You should know the properties of waves eg they all show reflection,refraction etc etc

Energy E=hf where h is the planks constant 6.63*10^-34, and f is the frequency

You need to know how to define the electron volt (eV): is the energy transferred when a electron moves through a p.d of one volt

In the exam it is common they ask you to show a phenomena which shows particle like behaviour of electromagnetic radiation and evidence for a wave nature. Examples are the photoelectric effect, interference and diffraction.
This is an important topic and I’m not excellent at it, show I would appreciate if someone posted some examples

Lastly you need to recall and use the de Broglie equation. Which is derived from einsteins E=mc^2 and plancks E=hf
By solving these two you should be able to show de broglies equation that de broglies wavelength= h/mc or =h/p

Electromagnetic Waves

Not too much to know on this topic but you should know that the electromagnetic spectrum includes radio waves, microwaves, infra red, visible light, ultra violet waves and gamma rays.

You should know all the features of the electromagnetic spectrum eg microwaves used to heat food, or gamma rays to cure cancer etc etc. you shoul also know all e.m waves travel at the same speed in free space ( a vacuum)

Lastly you should know the orders of magnitude of the wavelengths of all waves. Once again I would appreciate if someone posted these.

wave particle duality for an electron: (thanks to hihihihi)
wave behaviour:
-electrons travel/propagates/moves in space like a wave
-electrons shows diffraction/interference effects
- electrons maybe diffracted by matter- eg graphite, carbon atoms nuclei
-experimental evidece: rings/fringes
-diffraction of electrons when wavelength is comparable to gap size
-wavelength given by wavelength=h/mv
- where h=placnks, m=mass, v=velocity

particle behaviour:
-interacts with matter like a particle
-electrosn ahave mass
- electrons have charge
-electrons maybe deflected by electric fields/charges
-and by magnetic fields
-newtonian mechanics can be applied (eg F=ma)

Photoelectric Effect (thanks to neutrinohunter)

When light is shined on a metal surface the surface emits electrons.

Electromagnetic waves are made essentially of energy.

In terms of waves the amount of electrons emitted depends on the amplitude of the wave or the intensity and has increased/decreased frequency has no effect.

however in terms of particles, the number of electrons emitted depends on the energy which is Planck's Constant * Frequency (E = hf), here the amount of electrons emitted is proportional to the frequency unlike the waves model.

In different experiments by different people the results of whether light was a wave or a particle could not be proved.

Max Planck's model suggests light is a particle and Young's slit experiment suggests that light is a wave.

thanks for the notes (thanks to c4>07)
btw...

P=IV
V=IR ; I=V/R ; R=V/I

--> P=I^2R = V^2/R

(thanks to endeavour)
for Electrons&P, you need to know the wavelengths and corresponding frequencies of the electromagnetic spectrum. But only bother learning either frequencies OR wavelengths and use to calculate the other.

Tip:
If you have to convert between eV and joules, remember:
V=W/Q
=> W=VQ
or W = eV
ie W=(1.6*10^-19)V

thanks to Widowmaker
hf = work function + Ekmax
work function - the minimum amount of energy required to remove an electron from the surface of a material.
hf - the energy of the photon.
Ekmax - the maximum kinetic energy of the electron that has left the material (0.5m(vmax)^2)

Remember this paper is 90 marks from your final 300 in AS so it is 30% of your total mark. Most marks are gained on calculations so don’t make silly mistakes and always have lengths in metres. Quite a few marks are reserved for the qualitative question so learn those. Simple definitions can get you an easy 10 marks from 90 so learn all those.
2. if alot of people are doing this syllabus then i will post a thread for electrons and photons too, but it seems like most people do other exam boards
3. you are a total legend! I was beginning to think i was on my own with this one! heh.. im just doing f&m- a retake...!
4. (Original post by misty)
you are a total legend! I was beginning to think i was on my own with this one! heh.. im just doing f&m- a retake...!
yeh i'm doin a retake aswell. i only got 54/90 last time around, and this is not an extremley difficult module
5. ah cool.. what did u get overall?
I think i got like 72 for f&m, but finding A2 so much more difficult, I need as many points as I can from AS.
6. oh right.. whats 420, a B?
um.. ive got 248 atm.. twas my practical and waves which wasnt great, even after retake got like 90/120 i think. e&p was my best, got like 87/88... i havent done any f&m since the exam last year. ah well.. ill do it on sunday! planning to finish microbes and disease today, heh..
7. is there anyone else who does this module or does everyone else do edexcel?
8. i do ocr phy, does ney1 no off any gud websites for revision? i havent started yet!
9. the forces and motion notes where awesome, can u do 1 for module 2 and maybe wave properties...lol hope im not asking 2 much...this is much appreciated...bubyes
10. I do syllabus as as well - yes, the post is very much appreciated - I'll rep you when I get the chance. Threads for the other 2 units would be much appreciated too . I'm probably gonna leave my revisiong until the weekend, probably not the wisest thing to do...oh well.
11. um www.s-cool.co.uk is quite good- i used that for my AS last year.
12. if alot of people are doing this syllabus then i will post a thread for electrons and photons too, but it seems like most people do other exam boards
Anything concerning OCR Physics 2861/01 would be appreciated.

Interference, Photons, Quantum Mechanics and Path Difference type stuff mostly
13. For OCR Physics A, do you really have to know about time dilation?!
14. in A2 cosmo yeah!
15. i do OCR! have just started revising today, can manage forces and motion, its waves that im certain to fail...
16. lol i know exactly what u mean dude...like forces n motion and electrons n photons r gonna be ok,,, but waves is queer in the ass...lol nehow hope u do well
17. i dunno y but i found waves the easiest- theres hardly anything to learn is there? one u get ure head round it anyway. good luck on monday!
18. which exams do people have on monday? forces,electrons,waves?
19. I have the Mechanics/Waves/Quantum one.

So anything to do with Waves and Quantum behaviours would be greatly appreciated.
20. i have f&m, E&p, and W.P...n is it jsut me or have they shortened the exams??? i oculda sworn they were 1.30mins but its gonna be 1hr...but nm cya...damn stupid server is busy grrrr 1 more try

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