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

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Reply 40
Original post by CharleyChester
So yeah, revision is going well:



The hell is the little bloke at the bottom? :tongue:
Reply 41
Original post by soulcrasher
Do you guys know which way a diode should point in a circuit? Should we draw it following conventional current or electron flow?


The vertical line represents the cathode of the diode. That end of the diode must face the direction from which the negative current flow is coming.

http://www.ehow.com/how_5877369_check-direction-diode.html#ixzz1O1lwijrL
Original post by wibletg
The hell is the little bloke at the bottom? :tongue:


Thats de Broglie :biggrin:
Reply 43
Original post by CharleyChester
Thats de Broglie :biggrin:


Riiight :tongue:

He does have some crazy hair, does de Broglie
Original post by wibletg
Riiight :tongue:

He does have some crazy hair, does de Broglie


He seemed like the kind of guy to wear a top hat...?
Reply 45
Original post by CharleyChester
He seemed like the kind of guy to wear a top hat...?


Google him, he has some proper funky hair. :cool:
For the June 2009 paper, what diagram are we supposed to draw for the circuit in question 1)c)i) since the mark scheme isn't really clear :s-smilie:
Reply 47
For anyone interested I found a link to some well set out notes for this unit: http://milanmehta.net/ocrphysics/OCRPhysicsAG482RevisionNotes.pdf
Reply 48
Original post by davie18
For anyone interested I found a link to some well set out notes for this unit: http://milanmehta.net/ocrphysics/OCRPhysicsAG482RevisionNotes.pdf


Remind me to pos you tomorrow.
Reply 49
Original post by wibletg
Remind me to pos you tomorrow.

Also you can download it as a word document here if you want to make your own little adjustments. :smile:
Reply 50
Original post by davie18
Also you can download it as a word document here if you want to make your own little adjustments. :smile:


Cheers, that is one brilliant set of notes.
Hey,

Can someone please explain the origin of absorption and emission spectra. My teacher skipped it and i have no idea what they are or what the difference is.

Any help is much appreciated

Thanks
Original post by davie18
Also you can download it as a word document here if you want to make your own little adjustments. :smile:


Legend. Will +1 you when i have some to give :biggrin:
Original post by <XOXO>
Hey,

Can someone please explain the origin of absorption and emission spectra. My teacher skipped it and i have no idea what they are or what the difference is.

Any help is much appreciated

Thanks


Emission Spectra
Hot gasses produce line emission spectra
If a gas is heated, the electrons move to higher levels.
As they fall back down to ground state, they emit photons, producing line emission spectra with a black background with bright lines.
Each line corresponds to a particular wavelength of light emitted by the source.
Since only certain photon energies can be emitted, you only get the corresponding wavelengths.


Absorption Spectra
Cool gasses remove certain wavelengths from the continuous spectrum to produce an absorption spectrum
At low temperatures, most of the electrons will be at ground states.
Photons of the correct wavelengths are absorbed by the electrons to excite them to a higher energy level.
These wavelengths are then missing from the continuous spectrum when it comes from the gas
When looking at the sun, we do not see a full spectrum, this is because the light emitted by the sun must travel through the cooler outer layers of the sun’s atmosphere, as a result certain wavelengths are filtered out

Taken from the word document above :smile:
Original post by ebmaj7
Does hot gas just randomly get really excited and emit a photon? As in, the rate of photon emission is randomised?

Also, which way around do Light dependant resistors and Heat dependant resistors resist? eg. do LDRs resist when lots of light are falling on them, or when no light is falling on them?



Electrons are normally in the ground state, we say the electrons are in a excited state when they move up to a higher energy level.

I suggest you watch this video which explains in a simple way, graphically.
http://www.youtube.com/watch?v=kJBcXFsFa7Y

LDRs - As the light intensity on the LDR increases the resistance of the LDR decreases.

Thermistors (Heat dependant resistors lol) - As the temperature increases the resistance of the themistor decreases.
Reply 55
did anyone do the January 2011 paper?
can someone explain this to me:
i have heard somewhere that current always stays the same in a circuit and never gets used up.
but in some questions and diagrams it shows different currents and ... in confusing
Reply 57
Original post by Abused Tampon
can someone explain this to me:
i have heard somewhere that current always stays the same in a circuit and never gets used up.
but in some questions and diagrams it shows different currents and ... in confusing

It stays the same in a series circuit but it splits up in a parallel circuit.

Kirchoff's first law: "The sum of the currents entering a point = the sum of the currents leaving that point".

So in other words if you have a circuit that then splits into 2, if it had 10A before then it is impossible for them both to have 10A after splitting as this would break Kirchoff's first law.
Reply 58
Original post by Jukeboxing
I suspect these will be asked:

Electricity

Describe the uses and benefits of using light-emitting diodes.

Describe an experiment to obtain the I-V characteristics of a resistor at constant temperature, filament lamp and light emitting diode.

Define the Coulomb

Explain that electric current is a net flow of charged particles

Describe the difference betwen conductors, semiconductors and insulators in terms of the number density n.

Explain the meaning of the term Terminal P.d.

Waves

Explain what is meant by reflection and refraction.

State typical values for the wavelengths of the different regions of the EM spectrum.

Describe some practical uses of EM waves.

Recall and use Malus law

State principle of superposition

Apply graphical methods to illustrate the principle of superposition

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 similarities and differences between progressive and stationary waves.

Define and use the terms the fundamental mode of vibration and harmonics

Determine the speed of sound in air from measurements on stationary waves in a pipe closed at one end.

Quantum

Define and use the terms work function and threshold frequency.

Use einsteins equation hf = work function + KEmax

Explain that diffractions of elctrons by matter can be used to determine arrangements of atoms and size of nuclei

Describe origin of emission and absoption line spectra

Describe and experiment using LEDs to estimate plancks constant

Let me know if anythings been asked already or if i'm missing something.


Can someone write some quick answers to these?
Reply 59
Original post by Jukeboxing
I suspect these will be asked:

Electricity

Describe the uses and benefits of using light-emitting diodes.

Describe an experiment to obtain the I-V characteristics of a resistor at constant temperature, filament lamp and light emitting diode.

Define the Coulomb

Explain that electric current is a net flow of charged particles

Describe the difference betwen conductors, semiconductors and insulators in terms of the number density n.

Explain the meaning of the term Terminal P.d.

Waves

Explain what is meant by reflection and refraction.

State typical values for the wavelengths of the different regions of the EM spectrum.

Describe some practical uses of EM waves.

Recall and use Malus law

State principle of superposition

Apply graphical methods to illustrate the principle of superposition

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 similarities and differences between progressive and stationary waves.

Define and use the terms the fundamental mode of vibration and harmonics

Determine the speed of sound in air from measurements on stationary waves in a pipe closed at one end.

Quantum

Define and use the terms work function and threshold frequency.

Use einsteins equation hf = work function + KEmax

Explain that diffractions of elctrons by matter can be used to determine arrangements of atoms and size of nuclei

Describe origin of emission and absoption line spectra

Describe and experiment using LEDs to estimate plancks constant

Let me know if anythings been asked already or if i'm missing something.


These taken from the specification?

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