Post by: Linkage1992 on November 09, 2010, 07:09:43 pm
For instance, in vcaa 2007 i said that because the ratio was 1: 1.5, which I think is a fairly large deviation, there would not be significant diffraction, but the answers say there is. How far are you supposed to go??
Post by: kyzoo on November 09, 2010, 07:12:05 pm
Significant diffraction occurs when either 1.) wavelength is on the same order of magnitude as the gap 2.) wavelength is much bigger than the gap.
Post by: Linkage1992 on November 09, 2010, 07:15:19 pm
Post by: Chavi on November 09, 2010, 07:15:27 pm
Post by: 3Xamz on November 09, 2010, 07:19:11 pm
If its the same order = some diffraction
If its less than by 1 order = no diffraction.
Hence for wavelength/gap;
1) 1 or more = lot of diffraction
2) between 0.1 to 0.9 - some diffraction
3) <0.1 - no diffraction.
Post by: lachymm on November 09, 2010, 07:20:51 pm
Post by: 3Xamz on November 09, 2010, 07:22:18 pm
I just use a ratio of .1 to 10...Lamda doesnt have to be greater than or equal to width...significant diffraction occurs when the width is greater than the wavelength...
That sir, is not true.
Post by: Chavi on November 09, 2010, 07:23:15 pm
I just use a ratio of .1 to 10...Lamda doesnt have to be greater than or equal to width...significant diffraction occurs when the width is greater than the wavelength...other way around
Post by: TyErd on November 09, 2010, 08:51:40 pm
Post by: Chavi on November 09, 2010, 08:53:02 pm
if slit width is much smaller than the wavelength, that would mean there's a lot of diffraction right?yepp. Just remember that diffraction occurs when λ>w
Post by: TyErd on November 09, 2010, 09:07:42 pm
Post by: TyErd on November 09, 2010, 09:12:51 pm
Post by: superflya on November 09, 2010, 09:13:15 pm
Post by: TyErd on November 09, 2010, 09:17:21 pm
Post by: waack on November 09, 2010, 09:20:22 pm
Post by: TyErd on November 09, 2010, 09:25:51 pm
Post by: waack on November 09, 2010, 09:40:42 pm
Post by: m@tty on November 09, 2010, 09:46:39 pm
λ/w>1 so λ>w
The 2007 VCAA question said that a slit of width
So obviously we can't rely on the
Post by: TyErd on November 09, 2010, 09:50:10 pm
Post by: fady_22 on November 09, 2010, 09:51:59 pm
0.667 is pretty close to 1 so okay that's settled i guess, for significant diffraction has to be approximately 1, not greater
No, significant diffraction occurs when the ratio is greater than 1, however it is maximised when it is approximately equal to one.
Thats how I understand it, anyway.
Post by: waack on November 09, 2010, 09:54:27 pm
it actually says same magtitude of order which means when u convert the width of the gap and the wavelegth to m x 10^- (whatever number) if the number is the same for both they are of the same order and significant diffraction will occurλ/w>1 so λ>w
The 2007 VCAA question said that a slit of widthwill create significant diffraction with neutrons of wavelength
. They claimed that they were "of the same magnitude" and a diffraction pattern would form.
it says same 'order of magnitude' so when u convert the width and wavelength to m x 10^- (number) if the order being the number is the same for both in m then diffraction will be significant
So obviously we can't rely on therule.
Post by: Munkea on November 09, 2010, 09:54:33 pm
Not true, significant diffraction occurs when the ratio is approximately 1. For a value such as 0.6, significant diffraction would occur.0.667 is pretty close to 1 so okay that's settled i guess, for significant diffraction has to be approximately 1, not greater
No, significant diffraction occurs when the ratio is greater than 1, however it is maximised when it is approximately equal to one.
Thats how I understand it, anyway.
Post by: fady_22 on November 09, 2010, 09:55:41 pm
Post by: m@tty on November 09, 2010, 09:56:38 pm
Significant diffraction will occur if
Post by: TyErd on November 09, 2010, 10:09:44 pm
Post by: Ovalteenies on November 09, 2010, 10:13:52 pm
but is maximised at 1
Post by: fady_22 on November 09, 2010, 10:15:49 pm
Taken from the Heinemann book.
Post by: waack on November 09, 2010, 10:16:16 pm
Post by: TyErd on November 09, 2010, 10:18:24 pm
Since this ratio determines the spacing of the individual fringes, it determines the width of the overall diffraction pattern. The diffraction pattern will have a central fringe that is twice as wide as the other fringes. If the wavelength is held constant and the aperture or gap is made smaller, greater diffraction is seen. If different wavelengths enter the same gap, those with a small wavelength will undergo less diffraction than those with longer wavelengths. For example, the use of an aperture of a given width will result in greater diffraction of red light than blue light just as occurred with double-slit diffraction (Figure 11.15). Do not think of diffraction effects as suddenly occurring at a specific wavelength. Although we need λ ≈ w for a good diffraction pattern, diffraction will gradually increase if the values of λ and w are made to gradually approach one another.
Taken from the Heinemann book.
okay so that's maximised diffraction. What about significant diffraction?
Post by: fady_22 on November 09, 2010, 10:19:40 pm
Post by: TyErd on November 09, 2010, 10:29:06 pm
Post by: waack on November 09, 2010, 10:32:00 pm
Post by: TyErd on November 09, 2010, 10:38:17 pm
and more maximised diffraction, the order doesn't matter but it has to approximately equal 1?
is that right?
Post by: Linkage1992 on November 10, 2010, 12:02:51 am
So basically, for it to be maximized, the ratio has to be approximately 1, but simply for significant diffraction, they have to be of the same order magnitude. And with a wavelength greater than the size of slit the effect is more significant than when the size of slit is greater than the wavelength. got it.
good luck for today! :D
Post by: TyErd on November 10, 2010, 12:14:35 am