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

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got a C in a practice but a U in mechanics, need a strong C or B.

need help with:
maximum power efficency
light intensity
stationary waves
angle of diffraction

i know its alot but il be really grateful and will pos rep you when i can
:smile:

if you come up with specific things u need i can help, bit too vague with ure topics :smile:

Reply 281

shyro1000

Original post by Dale12

if you come up with specific things u need i can help, bit too vague with ure topics :smile:

i got the questions in the June 2010 paper,
2aiv, 3aii4, 3bii, all of 6c,

quite a bit :colondollar:

Reply 282

Dale12

Original post by shyro1000

i got the questions in the June 2010 paper,
2aiv, 3aii4, 3bii, all of 6c,

quite a bit :colondollar:

your in luck, i did that paper this morning and got 85 % :smile:

bare with me 1 second :smile:

Reply 283

shyro1000

Original post by Dale12

your in luck, i did that paper this morning and got 85 % :smile:

bare with me 1 second :smile:

ok thanks man :smile:

Reply 284

sweetascandy

Original post by Dale12

owe me some rep for this :wink:

nah its okay, basically you connect a string between a fixed point and connect it to a driving oscillator (basically it goes up and down really fast). this creates a progressive wave that reflects off the fixed point at a node (if you get the frequency tunes right). then using the idea of how a standing wave is formed you get a standing wave from a string :smile:

A standing wave is formed when a progressive wave reflects of a boundary resulting in two waves of the same wavlength travelling in opposite directions superimposing and causing a standing wave with nodes and anitnodes :smile:

its abit wordy but im just trying to explain it abit more :smile:

Lol, I've already told you: "You have reached the limit of how many posts you can rate today!" I will get back to you when I get a refill JUST to make you happy :p:

Thanks a lot :smile:

Btw, is a driving oscillator the same as a signal generator or a vibration generator or neither of them?

Reply 285

Jukeboxing

http://phet.colorado.edu/sims/photoelectric/photoelectric_en.jnlp

This is useful for understanding photocell circuit.

Reply 286

SamXi

Laws you need to know

Ohms law
The current in an ohmic conductor is proportional to the p.d across it given temperature and other physical conditions remains constant

Khirchy's 1st
The sum of the currents entering a junction = the sum of the currents leaving the junction
*this is the law which shows the conservation of charge

Khrichy's 2nd
The sum of the e.m.f's = the sum of the p.d's in a closed loop

Malus' law
If one polarized lens is placed in front of another the intensity of the light is proportional to cos^2(theta) of the angle which the second lens is rotated

I=Imax x Cos^2(Theta)

(edited 12 years ago)

Reply 287

Dale12

Original post by shyro1000

i got the questions in the June 2010 paper,
2aiv, 3aii4, 3bii, all of 6c,

quite a bit :colondollar:

2.a.iv ) 1 - is just 1/R = 1/R1 + 1/R2 where u r given R of the 60W in the question and you worked out R of the 25W in part a.ii
2 - V=IR, using R form the combined resistance in part 1
3.a.ii) 4 - E=V+Ir rearrange to get ... (E-V)/I = r.... used point b as your V and I values
3.b.ii) intensity x Area = p... then calculate the % difference between your power value and the 0.25W value
6.c) i and ii are just describing the displacement at those distances, e.g fig6.2 has maximum displacement at 0
and fig 6.3 at 0 and 4 there are antinodes where displacement is a maximum..
Hope that helped :smile:

Reply 288

Jukeboxing

Original post by SamXi

Annnddd....

Amplitude = amplitude0 x cos(theta)

Coulombs Law

Nahh, you dont need to know that.

(edited 12 years ago)

Reply 289

Dale12

Original post by sweetascandy

Lol, I've already told you: "You have reached the limit of how many posts you can rate today!" I will get back to you when I get a refill JUST to make you happy :p:

Thanks a lot :smile:

Btw, is a driving oscillator the same as a signal generator or a vibration generator or neither of them?

JUST to make me happy eh :smile:

a driving oscillator just waggles the string up and down... basically the same as a vibrations generator :smile:

Reply 290

shyro1000

Original post by Dale12

thanks man :biggrin:

your a legend, that really helped. il pos rep you tomorrow in return.
just hope these come up in the exam now :smile:

Reply 291

SamXi

Original post by shyro1000

i got the questions in the June 2010 paper,
2aiv, 3aii4, 3bii, all of 6c,

quite a bit :colondollar:

6c
i) From left to right: Max motion then decreases each increment until no motion at 0.6
ii) From left to right: Max, none, Max, none

We know this because where the wave is at its highest point is an anti-node which is a point of constructive interference resulting in max particle movement and the point where there is no displacement ( where it touches the line) is a node which is destructive interference meaning no motion occurs

Reply 292

Dale12

Original post by shyro1000

thanks man :biggrin:

your a legend, that really helped. il pos rep you tomorrow in return.
just hope these come up in the exam now :smile:

cheers mate :smile:

good luck tomorrow, afternoon exam so get a lie in haha :smile:

thats my plan anyway :biggrin:

Reply 293

SamXi

Original post by Jukeboxing

Annnddd....

Amplitude = amplitude0 x cos(theta)

Coulombs Law

Nahh, you dont need to know that.

FML u actually had me worried then

Reply 294

Jukeboxing

Original post by SamXi

FML u actually had me worried then

Reply 295

shyro1000

Original post by Dale12

cheers mate :smile:

good luck tomorrow, afternoon exam so get a lie in haha :smile:

thats my plan anyway :biggrin:

you too, let me know what you thought of it on here or PM me. nah full revision for me bud

Reply 296

levantine

Original post by Wilko94

Can someone explain to me the relationships between current, voltage, and resistance.

eg.

- If you change the voltage supplied, how does the resistance and current change?
- If you increase the resistance, does the current decrease but the voltage stay the same?

Struggling to get my head round all this!

remember voltage is proportional to resistance. so as voltage increase so does resistance therefore current stays the same.