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The Physics PHYA2 thread! 5th June 2013

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not sure if this will help, but i posted it earlier:

Here are some key points i made for all of you for PHYA2 to bare in mind:

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Forces acting on an object in equilibrium form a closed loop (Vector triangle)

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Define moment: force x perpendicular distance, and is the turning effect of a force around a turning point.

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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.

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Torque = Force (Turning force) x perpendicular distance between them.

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gives the gradient on a curve to be velocity. and since is acceleration, therefore the stepper the curve the greater the acceleration.

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Newton's First Law: An object will stay at rest or in uniform velocity, unless a resultant foce acts on it.

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Newton's Second Law: Acceleration is proportional to the resultant foce acting on it at a certain mass. F=ma

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Newton's Third Law: When 2 objects interact, they exert an equal and opposite force on eachother.

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Free fall is when the only force acting on an object is gravity.

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For projectile motion: VERTICAL you use SUVAT, for HORIZONTAL you use and in both cases 't' is the same.

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When Friction force = Driving Force object stops accelerating and reaches its terminal velocity.

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Types of friction: Contact (Friction), Fluid (Drag, Air resistance, Fluid Resistance)

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Principle of conservation of energy: Energy cannot be created or destroyed, but can be transferred from one form to another.

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

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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).
5) follow same steps when unloading.
6) Repeat experiment 3 times taking an average result.
7) Plot a graph of force against extension to show results.

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Elastic and Plastic deformation: If elastic, material will return to original length. Elastic when material will not return to original length

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Young Modulus:

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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 =

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Waves are vibrations, they only carry and transfer energy.

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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

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Phase difference: Amount by which one wave lags behind another wave.

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Transverse waves: Vibrations oscillating at right angles to the direction of travel (Electromagnetic waves, waves on rope, ripple of water ...etc)

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Longitudinal waves: Vibrations oscillating along direction of travel (sound)

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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.

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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.

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Signal loss (reduction in amplitude) in optical fibres are caused by energy lost through absorption and scattering.

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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.

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Principle of Superposition: When 2 or more waves cross, the resultant displacement equals the vector sum of the individual displacement.

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Constructive interference: when displacement combine to make an even bigger one (e.g. crest plus crest)

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Destructive interference: when negative and positive displacement combine to cancel out (e.g. crest plus trough)

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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 ...

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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

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Application of stationary waves: Microwaves, sound waves.

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you get greatest diffraction if the slit size is equal to

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Laser is monochromatic (has a single wavelength) and coherent (same frequency and constant phase difference).

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laser beams are powerful and can cause damage to eyesight, this can be prevented by wearing safety laser goggles or removing any reflective surfaces.

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Path Difference: how much further a wave has travelled than the other wave.

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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 .

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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).

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non - coherent light such as white light will have wider maxima containing different colours with central white fringe. light is continuous range of frequencies

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Young's double slit experiment: . w is fringe spacing. is wavelength, s is spacing between slits, and D is distance from slits to screen.

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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 !!!!!

OMG! Life saver!! thank you so much!

Reply 681

taliaa

help please! jan 2012,
question 2 b i

I got the 3700+5300 for total energy, but how do you calculate wasted energy?

Reply 682

StalkeR47

Original post by ammara_12

could you explain the youngs modulus experiment to me please :colondollar:

LOL! Ok, ----------Young modulus experiment was done to test the properties of different types of materials. Check this video out! It explains everything! http://www.youtube.com/watch?v=qvcpeA5pBH0 :colondollar:

Reply 683

masryboy94

Original post by taliaa

help please! jan 2012,
question 2 b i

I got the 3700+5300 for total energy, but how do you calculate wasted energy?

it is the energy input - energy output: so in this case in part)a)ii) and iii) we worked out the Kinetic energy the e bike had at B which was

1.9\times10^3 J

and its gain of gravitational potential energy up to point B which we got to be

2.4\times10^3 J

are the energy outputs. so what you do is

(3700 + 5300) - (1.9\times10^3 + 2.4\times10^3) = 4.7\times10^3 J

and that is your energy wasted :biggrin:

(edited 10 years ago)

Reply 684

StalkeR47

Original post by taliaa

help please! jan 2012,
question 2 b i

I got the 3700+5300 for total energy, but how do you calculate wasted energy?

You again! AHHHHHH!!!!! :angry:

-------------- GPE=2400j, Ke=1900J, Electric motor=3700j. What is the total energy input? well, you have cyclist pedalling at 5300j (input power to move to a certain distance) and you have electric motor od 3700j. Add them together to get total input power. Answer is 9000j. Remember, (input - output = wasted energy). What is the output energy? GPE and KE are the output energies. so, 1900(ke) + 2400 (GPE) = 4300j. so, input - output = wasted------9000-4300=4700j. :smile:

Reply 685

masryboy94

Original post by StalkeR47

DR PHYSICS IS A LEGEND !! loool

Reply 686

StalkeR47

Original post by masryboy94

DR PHYSICS IS A LEGEND !! loool

HAHA! He messes up the latters sometimes. :biggrin:

Reply 687

masryboy94

Original post by ammara_12

OMG! Life saver!! thank you so much!

haha no worries, anything to help outt !! just hope its made you understand the things you were confused with :redface:

Reply 688

masryboy94

Original post by StalkeR47

HAHA! He messes up the latters sometimes. :biggrin:

yeh he does, i used him alot for PHYA4 ! he goooood

Reply 689

StalkeR47

Original post by masryboy94

yeh he does, i used him alot for PHYA4 ! he goooood

PHAY4? Are you yr 13? So you are resitting these exams right? :smile:

Reply 690

ammara_12

I am hoping those lift questions don't come up in this paper :frown:

Reply 691

masryboy94

Original post by StalkeR47

PHAY4? Are you yr 13? So you are resitting these exams right? :smile:

yuup, did okay in that exam in yr 12, but i got told by my teacher to be certain of atleast an A overall, it would be easier to get those 'extra' UMS from phya2 rather than pressure myself too much on phya5.

p.s. whoever decides to carry on physics into A2 and is finding AS difficult or challenging, i think its good for me to say that you will NEEEEEEEEEEEEEEEEEED to revise from september, especially with PHYA4, it was soooo hard omg !!

Reply 692

masryboy94

Original post by ammara_12

I am hoping those lift questions don't come up in this paper :frown:

as much as you 'hope' ... don't regret not knowing it, imagine it comes up and you know those questions have like 4/5 parts to it each worth around 2/3 marks. so whatever you don't understand about it or struggle with. now is your best time to ask !! that is what TSR is for :biggrin:

Reply 693

Anythingoo1

Does anyone have a step by step guide for proving the diffraction grating equation?

Am willing to exchange for sexual favours :colone:

Reply 694

Calrooke

Original post by posthumus

overall at AS ... 240/300

and 96/120 in each examination (unit 1 & 2)
48/60 is an A in the ISA

Thanks a lot!

Reply 695

StalkeR47

Original post by masryboy94

Thanks man! Thanks for encouragement! Very appreciated! Good luck to you! And, which university are you going to?

Reply 696

masryboy94

Original post by Anythingoo1

Does anyone have a step by step guide for proving the diffraction grating equation?

Am willing to exchange for sexual favours :colone:

putting aside the sexual favours :tongue:

here goes:

lets say the distance between the centre of 2 adjacent slits is 'd' which can be worked out by doing

\frac{1}{no.of.slits.per.metre}

. so as the wavefront of the source comes in, it diffracts at an angle

\theta

towards the screen, this can be calculated by using a protractor or a spectrometer. if you get constructive interference you know that the path difference for say the first order is

\lambda

. now using some trig, we know that

sin\theta = \frac{opposite}{hypotenuse}

. sub in

\lambda

and 'd' to give

sin\theta = \frac{\lambda}{d}

. which gives

dsin\theta = \lambda

. now for every maxima or order on the screen, that means you are getting constructive interfence, therefore the path difference with always have to be a whole number (integer) multiple of