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# OCR Physics A G482, Electrons, Waves and Photons, 25th May 2012 Tweet

Physics exam discussion - share revision tips in preparation for GCSE, A Level and other physics exams and discuss how they went afterwards.

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1. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by choc_1209)
i cant open this document?!
Hmm seems fine to me. What happens when you try to open it?
2. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by the real viper)

Explain the meaning of the term Terminal P.d.

The potential difference across a source. Not too sure on this one any suggestions??.
Terminal p.d. is the potential difference across the external resistor connected to an EMF source. This is the definition which I've learnt
3. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by the real viper)
State typical values for the wavelengths of the different regions of the EM spectrum.

Microwaves: 10^-3 -------- 10^-1 Radar, microwave cookery, TV transmissions
Infrared: 7x10-7 -------- 10^-3 Night-visions, optical fibres, remote controls
Ultraviolet:10^-8 ------- 4x10^-7 Sunbeds, Security Markings
X-Rays: 10^-13 ------- 10^8 See damage to bones, Kill cancer cells
Gamma Rays: 10^-16 -------- 10^-1 Irradiation of food, Sterilisation, Chemotheraphy
You missed out visible light btw. Its wavelength is 4x10^-7 (blue) to 7x10^-7 (red). And its uses are: sight, communication, photography and signalling.
4. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
:| I keep sweeping this exam under the rug The majority of it is electrical calculations which I struggle to revise for as they're different each time (Kinda the point I know!) Mainly been trying to remember all the definitions - particularly the wave ones

I think I have the quantum bit down so it's mainly electricity I need to focus on - anyone have any good summarising tips for electrical stuff?
5. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by davie18)
Hmm seems fine to me. What happens when you try to open it?
when i save it its fine but when i open it or when i directly open it without saving it says the file is corrupt and to open it thorugh 'open and repair' and even when i did that it comes up as corrupt file etc?
6. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
Energy levels. Can somebody try to explain them to me, no matter how many times I read about them in the textbook, I simply can't get my head around them. I would really appreciate it cheers !

Also, the grade boundaries for this paper are so low, surely if you get all the easy 1-4 mark questions correct, which are mostly just recalling facts and rearranging formula's you should be at an A already.
7. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
can someone list the formulas that we must remember which are not going to be on the formula sheet!!
8. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by Jukeboxing)
You got those mixed up.

I've just done the question and for

7 degrees: 3.3x10^-6 x sin(7) = 4.02..x10^-7m (about 402nm) which is the wavelength for U.V

12 degrees: 3.3x10^-6 x sin(12) = 6.86...x10^-7m (686nm) which is the wavelength for Red.

From Red to Ultra violet the wavelength decreases.

Oops, kind of a fundemental thing to know

Thanks
9. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
Can anyone outline the experiments we'll be expected to know/describe/draw?
Because I know them roughly but when I'm doing practice papers I'm struggling to get full marks because I don't know exactly what OCR want us to put.
10. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by sweetascandy)
Terminal p.d. is the potential difference across the external resistor connected to an EMF source. This is the definition which I've learnt
So what happens if there is multiple resistors all with different resistance? Is the terminal pd the individual pds of each resistor or the summed pds of each resistor?
11. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by A for Andromeda)
Oops, kind of a fundemental thing to know

Thanks
did the mark scheme just have uv or could you say blue?
12. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by zonka)
can someone list the formulas that we must remember which are not going to be on the formula sheet!!
intensity = amplitude^2
intensity = power/ cross sectional area
frequency = 1/time period
EMF= IR + Ir
EMF= I(R + r)
EMF= V + v
Malus Law: A= A0 cos theta & I= I0 cos^2 theta

think that is it
13. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by the real viper)
So what happens if there is multiple resistors all with different resistance? Is the terminal pd the individual pds of each resistor or the summed pds of each resistor?
Urmm I'm not really sure; on the spec it says to just know the equation but I'm guessing it would mean the sum of the pd's!
14. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by Toshiya)
Can anyone outline the experiments we'll be expected to know/describe/draw?
Because I know them roughly but when I'm doing practice papers I'm struggling to get full marks because I don't know exactly what OCR want us to put.
Describe an experiment to obtain the I-V characteristics of a resistor at constant temperature, filament lamp and light emitting diode.

Describe Experiments that demonstrate two-source interference using sound, light and microwaves.

Describe Young double slit experiment.

Describe experiment to determine wavelenght of monochromatic light.

Describe and experiment using LEDs to estimate plancks constant - (The photoelectric effect basically!)

ENJOY!
15. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by sweetascandy)
Urmm I'm not really sure; on the spec it says to just know the equation but I'm guessing it would mean the sum of the pd's!
Wait i've just read that the you sometimes take the terminal pd to be the EMF of the supply because you are ignoring internal resistance so therefore the terminal pd must be the sum of the individual pd's i guess!!!
16. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
Grade boundaries are so low on this paper, have found some of the more recent ones just stupid though, overly vague and focusing on areas that aren't really covered in the book or anything.
17. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by WillKail)
Grade boundaries are so low on this paper, have found some of the more recent ones just stupid though, overly vague and focusing on areas that aren't really covered in the book or anything.
agreed, as long as you are getting all the calculations correct and then getting like 2/3 of the explanation questions (sometimes less) you've basically got an A
18. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by welshy93)
did the mark scheme just have uv or could you say blue?
Only blue/violet - but I'm fairly sure it meantioned something about it being visible (light) in the stem of the question
19. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by OllyHV)
Energy levels. Can somebody try to explain them to me, no matter how many times I read about them in the textbook, I simply can't get my head around them. I would really appreciate it cheers !
- Each element has a unique spectra (of wavelengths).
- Isolated atoms are gas atoms that exert negligible forces on each other. So they absorb/emit light photons of different frequencies, (which is evident from their absorption and emission spectra).
- If you heat a gas, many electrons move to higher energy levels (since they gain more heat energy).
- Absorption line spectra arise when EM radiation is absorbed by isolated atoms. An electron absorbs a photon of the correct energy to allow it to make a transition to a higher energy level. When an electron moves down an energy level, it emits a photon.
- At cool temperatures, electrons are most likely to be at the ground state.

Feel free to correct me where I'm wrong; I don't feel that confident on this topic myself tbh! But I hope it does help someone
20. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by A for Andromeda)
Only blue/violet - but I'm fairly sure it meantioned something about it being visible (light) in the stem of the question
ohh ok thankss
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