I hate VCAA and TSSM

[danielf]

VCAA had a massive bitch last year about light diffraction: They said significant diffraction only occurs when the width of the obstacle is ofthe same order of magnitude as the wavelength (ie both x10^10, etc)
I came across a question in the TSSM paper that said:
a 200keV beam undergoes moderate diffraction whilst 110pm X-rays diffract significantly when passed through the same slit. What is the best approximate for the width of the slit.
A/B were retarted
C: 2x10^-12m
D:2x10^-10m
I thought the answer would be D b/c it is of the same order of mag as the wavelength. TSSM says its C and I have no idea why

[ReVeL]

110pm = 110 picometres =

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Yeah no idea why its C. Possibly a dodgey question...

[bturville]

btw...is this the precursor to a fuck VCAA thread?

[onlyfknhuman]

VCAA had a massive bitch last year about light diffraction: They said significant diffraction only occurs when the width of the obstacle is ofthe same order of magnitude as the wavelength (ie both x10^10, etc)
I came across a question in the TSSM paper that said:
a 200keV beam undergoes moderate diffraction whilst 110pm X-rays diffract significantly when passed through the same slit. What is the best approximate for the width of the slit.
A/B were retarted
C: 2x10^-12m
D:2x10^-10m
I thought the answer would be D b/c it is of the same order of mag as the wavelength. TSSM says its C and I have no idea why

The question asked for significant diffraction hence :  wavelength / w   greater/equal to  1

What your talking about in terms of VCAA is where diffraction just occurs for the light/matter section only which is if it is greater then or equal to .001 [note that for sound it is 1]

Since 110 x 10^-12 = 1.1x10^-10 

wavelength / w > 1 for significant diffraction 

wavelength / w > .001 for minimum diffraction

1.1x10^-10 / 2x10^-12 = 55

1.1x10^-10 / 2x10^-10 = .55

You choose which is bigger?

hence significant diffraction as its > 1

Hope this helps - SOMEONE CLARIFY THIS I HAVNT TOUCHED PHYSICS IN WEEKS

VCAA can screw it self cant believe i fckn got a B+ for mid year. was aiming for a 40+ -_-...

[danielf]

Are u sure? cos my textbook and VCAA makes no mention of 0.001 for diffraction (just 1) and anyway, 0.55 is closer to 1 than 55 so would the .55 one diffract more. huh? what? i'm really lost now

[onlyfknhuman]

This was mention in the ass report, as well as the herald sun and the age 2008 VCE guide. One of those two mentioned it. That many students got confused sound diffraction with Light diffraction.

its not a matter of whats closer to one, its a matter of whats greater or less then 1.

SIGNIFICANT DIFFRACTION OCCURS when the WAVELENGTH / WIDTH ratio is GREATER THAN or equal to one  <- Remember this . for both LIGHT AND SOUND.

HOWEVER, this is where it differs.

Diffraction does occur for SOUND but much less and is unnoticeable when the ratio of WAVELENGTH/WIDTH is LESS THAN 1

Diffraction does OCCUR for Light however if the ratio of WAVELENGTH/WIDTH IS GREATER THAN .001 or if the Wavelength and width is the same MAGNITUDE which you stated above eg. 2x10^-10  and 3x10^-10  =  same magnitude

ps. if your using heinemin physics text book. i suggest you burn it, burn it good. i hate it to shits. i even burnt my own one. didnt even touch it for unit 4.

[danielf]

ha ha look up marcellin in the herald sun website - apparently we had a book burning thing going on so maybe i will bring my heinimann there
i think that its starting to make sense though - when the width = order of mag of wavelength of SOUND, little diffraction occurs (wavelength has to be much bigger to diffract)
when the width = order of mag of wavelength of LIGHT, lots of diffraction occurs and as the wavelength increases, diffraction increases even more
is this right?

[onlyfknhuman]

No lol i suggest you re-read i'll re-word it see if you can understand a bit better so hold on

[onlyfknhuman]

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  =   note: i changed this sorry i made an error >_<



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[Captain]

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  =   note: i changed this sorry i made an error >_<



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As you get too far above 1, this breaks down.  The ratio has to be as close to 1 as possible, to get really good diffraction.

[onlyfknhuman]

really? never knew that. to what extent ' above 1'