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Physics 9702 Paper 4 Preparation and Sure Questions

Wasim Mohammed

Wasim Mohammed

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Natitah18 said:
Do you mind posting notes about Section B? Preferbably notes on Direct Sensing. Thanks!
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Here are some notes on Direct Sensing

EQUATIONS:
Vout = A0 ( V+ - V- )
Inverting amplifier : Vout/Vin = -(Rf/Rin) (need to derive)
Non inverting amplifier : Vout/Vin = 1 + (Rf/R1)

Definitions:
Negative feedback:
Process whereby a fraction of the output is fed back to the inverting input
Infinite input impedance:
No current enters or leaves either of the inputs
Zero output impedance :
The whole of the output voltage is seen across the load connected to the output
Infinite bandwidth :
All freq. are amplified equally
Infinite slew rate:
No time delay between changes to input and output
Infinite open loop gain:
There is only a very small difference in input voltage before amplifier saturates.

Additional Information :
Negative feedback produces
-Increased bandwidth
-Less distortion of the output
-Greater stability
Inverting amplifier
-Non inverting input earthed and negative feedback
Non inverting amplifier
-Both inputs not earthed
Output devices
-Relay- an electromagnetic switch
-LED- semiconductor device - used as indicator

These are simplified notes. I hope that this will help u . I will try to post more notes
again if any comments or feedbacks. pls do so . thank u :D
 
Wasim Mohammed

Wasim Mohammed

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KeshPal said:
Umm some notes on quatum physics maybe?
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Heres some notes on quantum physics

Equations :
E=hf (only for photons)
c=fλ
work function = hf0
E photon = Work function + KEmax
(Ek)max against f (gradient=h)
hf= hf0 + (Ek) max
(Ek) max = hf - hf0
E photon emitted = E2 - E1
λ= h/p

Definitions:
Photon : Discrete packets of energy of electromagnetic radiation with the energy given by E=hf where h=Planck's Constant and f= frequency of electromagnetic radiation
Threshold Frequency : Minimum freq. of electromagnetic radiation for electrons to be emitted from the metal surface
Work Function : Minimum energy of a photon needed for an electron to escape from the metal surface

Additional Information:
-Photoelectric emission : evidence from particulate nature of e.m. radiation
-Instantaneous emission
-Min. freq. for photoelectric emission to occur (threshold freq.)
-Max. K.E independent of intensity but dependent on frequency
-Rate of emission of electrons (photocurrent) proportional to intensity

-Wave theory:
-May be a time delay for electrons to collect enough energy before escaping
-Electrons should be able to escape from metal as long as the exposure time is long enough to allow it to collect enough energy regardless of the frequency of the wave

-Quantum theory:
-Photon energy depends on freq. (E=hf)
-Emission of electrons take place as long as the photon energy > energy needed to remove electron from the metal surface (work function)
-Hence there is a min. freq. (threshold freq.) of which any photon below that would not cause emission of electron from the surface

-Photoelectric emission:
-Range of K.E of electrons emitted : Max K.E for electrons at metal surface . Electrons deeper inside the metal requires more energy to escape
-Intensity = ((Total energy/time)/Area) =(E1 photon x no. of photons ) and total energy depends on λ and f .

-Electron Diffraction : evidence for wave nature of particles
-Experiment:
-Electron Beam in a deflection tube (vacuum inside) incident on a thin graphite sheet
-Fluorescent screen
-Observation : Concentric bright and dark rings are seen instead, showing diffraction of electron similar to the diffraction of visible light
-(if electrons are particles, should see a bright dot of uniform distribution)
If speed of electron Increases, (p=mv= h/λ) , p increases, λ decreases , ring diameter decreases as dsinθ=nλ

-De Broglie's relation
-Every moving particle has its own associated wavelength given by λ=h/p where λ = De Broglie wavelength ,h= Planck's Constant and p=momentum

-Line spectrum: Evidence for existence of energy levels
-Emission line spectrum : Low pressure gases
-Each line corresponds to photons of particular wavelengths
-Discrete wavelengths corresponds to photons of particular energies (E=hf)

These are simplified notes. I hope that this will help u . I will try to post more notes
again if any comments or feedbacks. pls do so . thank u :D


 
Wasim Mohammed

Wasim Mohammed

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TimBluesWin said:
I expect it to be not that high... The questions are completely different.... Probably around 53 something for A....
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I guess so it would be around the range of 51-53. bcos some of the easier papers in oct-nov 2013 had a threshold of 55 for an A . Let's all hope for the best :D
 
TimBluesWin

TimBluesWin

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Wasim Mohammed said:
I guess so it would be around the range of 51-53. bcos some of the easier papers in oct-nov 2013 had a threshold of 55 for an A . Let's all hope for the best :D
Click to expand...
If you said that last oct/nov was easy, then this year should be lower.... Probably now I would say 49-51.
 
P

PE Lim

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I think I messed up with this A2 Physics ...
I'm taking 43 variance too , and its like WHAT ?!! for the whole two hours on Monday ...
I'm not a very good student , but still I did the revision and done the past year ...
And it came out whole different than past year ... plus I have headache on that morning ...
Then it end up disaster for my exam , not even sure I can get 20 marks ......
Is anyone know about the threshold ? I'm very scared I'll get a U/E because to me that's totally possible now ...
 
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