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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 Joseppea)
Thank you!!! Now just gotta hope it comes up tomorrow...

Also, question for whoever knows it, is an absorption spectrum mostly black with a few coloured lines or mostly coloured with a few black lines? o.O
This may summarise it for you:
- A line spectrum = a series of bright light against a dark background.
- An absorption spectrum = a series of dark lines appear against bright backgrounds.
2. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by SamXi)
Gonna dump all the experiments i know ... someone correct me if i miss something out pls !

Photoelectric effect
-one photon acts with one electron
-if the photon is below the threshold frequency no electrons are displaced even if the intensity is altered
-if the photon is above the threshold frequency a surface electron is freed
-when the frequency is above the threshold the amount of electrons displaced is effected by intensity
-if the kinetic energy transfered from the photon to the electron is great enough it will travel through the vacuum to complete the circuit

Stopping potential
The stopping potential can be found by passing a current the opposite direction to the freed electron, by finding the point where both cancel each other out you can find the KE of the electrons
Hey you know the experiment where the circuit is used for measuring kintetic energy of photoelectrons (p174 in the book) could you please explain it to me? I dont get the whole p.d. thing
3. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by jake9382)
thankss soo if vibrating air produces longitudinal wave then how does the whole transverse wave come into the situation? Is there a longitudinal and tranverse wave?
When you pluck a violin string, it makes a sound. The sound is longitudinal, like any other sound wave.

However, if you ignore the sound, and look at the string, the string has a longitudinal wave going through it.

Like when you pluck an elastic band or something. The string goes up and down and makes a sorta stretched oval shape. There is a longitudinal wave going through the string.

• Progressive wave is reflected at the edge of the violin.
• Reflected wave superposes with incident wave.
• The two waves interfere with each other.
• Where destructive interference takes place, nodes are produced.
• Where constructive interference takes place, antinodes are produced.
4. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by jake9382)
Hey you know the experiment where the circuit is used for measuring kintetic energy of photoelectrons (p174 in the book) could you please explain it to me? I dont get the whole p.d. thing
I dont have the book mate.. but i think thats stopping potential which ive explained above il try and go into more detail

- The stopping potential can be found by passing a current the opposite direction to the freed electron
- To find the max KE of an electron we need to know find voltage is needed to cancel out the photoelectron
- We then multiply the voltage by e (electron charge / 1.6x10^-19) to find energy
Last edited by SamXi; 05-06-2011 at 20:49.
5. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by ebmaj7)
When you pluck a violin string, it makes a sound. The sound is longitudinal, like any other sound wave.

However, if you ignore the sound, and look at the string, the string has a longitudinal wave going through it.

Like when you pluck an elastic band or something. The string goes up and down and makes a sorta stretched oval shape. There is a longitudinal wave going through the string.

• Progressive wave is reflected at the edge of the violin.
• Reflected wave superposes with incident wave.
• The two waves interfere with each other.
• Where destructive interference takes place, nodes are produced.
• Where constructive interference takes place, antinodes are produced.
THANKKKS I get it noww
6. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by Dale12)
with 2 source interference, you move the probe along the 'screen' (where the screen would be in youngs double slit) and you'll get the interference pattern...

however to detect a stationary wave you move it between the transmitters and the metal sheet, sort of back and forth and you will be able to detect low signal (node) and high signal (antinode)

also the 2 source interference uses two transmitters connected to one source, for stationary waves only 1 transmitter is used to reflect off a metal sheet... that help?
Do you know an experiment for stretched strings forming stationary waves?
7. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
anyone know the experiments we need to know?
8. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by shyro1000)
anyone know the experiments we need to know?
Check this thread a couple of pages back - lots of experiment comments
9. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by SamXi)
I dont have the book mate.. but i think thats stopping potential which ive explained above il try and go into more detail

- The stopping potential can be found by passing a current the opposite direction to the freed electron
- To find the max KE of an electron we need to know find voltage is needed to cancel out the photoelectron
- We then multiply the voltage by e (electron charge / 1.6x10^-19) to find energy
cool thanks a lot
10. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by Joseppea)
Check this thread a couple of pages back - lots of experiment comments
ah ok thanks bud
11. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by shyro1000)
anyone know the experiments we need to know?
Look at my post on the previous page .. im adding all the ones i know

-two slit
-find planks constant
-speed of sound
-photoelectric effect
-gold leaf spectrometer photoelectric effect
-Voltage/current graphs
-de broglie diffraction
12. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
So, to find the I-V characteristics of a resitor, lamp, LED, how do you set up the circuit? i know it's something to do with a potential resistor, and a voltmeter in parallel with component you're testing, but...

mark schemes seem to differ, one said that you couldn't just set up the PR in series with the component (and then the voltmeter in parallel with just the component), and i can't see why this is wrong or how i should draw it to make it correct.

Anyone know?
13. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
what time is the exam 2moz??? is it 9 or 2
14. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
Does anyone else feel as though this exam is mainly based upon regurgitating information?
15. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by ngnav)
what time is the exam 2moz??? is it 9 or 2
i got it a 1:30
16. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by shyro1000)
i got it a 1:30
thats strange coz all our exams either start at 9 or 2
17. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by sweetascandy)
Do you know an experiment for stretched strings forming stationary waves?
when u connect a string to a driving oscillator connected to a fixed end.... do you know that experiment?
18. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by ngnav)
thats strange coz all our exams either start at 9 or 2
my college do them at 9 or 1:30, maybe a school/college thing?
19. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by WarpStreak)
So, to find the I-V characteristics of a resitor, lamp, LED, how do you set up the circuit? i know it's something to do with a potential resistor, and a voltmeter in parallel with component you're testing, but...

mark schemes seem to differ, one said that you couldn't just set up the PR in series with the component (and then the voltmeter in parallel with just the component), and i can't see why this is wrong or how i should draw it to make it correct.

Anyone know?
At college we've been taught to just put the voltmeter in parallel to the the resistor and an ammeter in series with it

But in my revision guide it shows the potential divider way to set it up

The potential divider circuit is better (i cant remember the reason off the top of my head) but both will work.
20. Re: OCR AS - Physics Unit G482 Electrons, Waves and Photons REVISION!
(Original post by WarpStreak)
So, to find the I-V characteristics of a resitor, lamp, LED, how do you set up the circuit? i know it's something to do with a potential resistor, and a voltmeter in parallel with component you're testing, but...

mark schemes seem to differ, one said that you couldn't just set up the PR in series with the component (and then the voltmeter in parallel with just the component), and i can't see why this is wrong or how i should draw it to make it correct.

Anyone know?
have a variable resistor in series with the component ure testing, have a voltmeter across the component and an ammerter in series with the component... adjust the variable resistor and plot the values of current and potential difference..
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