Post by: Xavier1234 on November 10, 2010, 01:58:00 pm
Post by: curious111 on November 10, 2010, 01:59:24 pm
Post by: tkjnz on November 10, 2010, 01:59:37 pm
Post by: zackyjack on November 10, 2010, 02:04:06 pm
Post by: Xavier1234 on November 10, 2010, 02:04:35 pm
Post by: rubiks on November 10, 2010, 02:17:40 pm
Post by: Elnino_Gerrard on November 10, 2010, 02:19:30 pm
I got 24761. All my friends said they got 12000 or something. They said the speed of the electron was the same as the previous question but when I worked it out I got a speed that was different.Yes thats what i got :D
Post by: Galvanic Cell on November 10, 2010, 02:19:35 pm
Post by: 3Xamz on November 10, 2010, 02:20:45 pm
First I was like no way, then I worked out that the energy of a x-ray can range between 500ev to 1*10^5,
so then I left it as the 2.something*10^4
Post by: curious111 on November 10, 2010, 02:20:59 pm
how did you get the speed from the energy?
600 x 1.6*10^-19 is the energy in joules. Then use (1/2)m*v^2 to find speed.
Post by: m@tty on November 10, 2010, 02:21:06 pm
Then since X-rays are electromagnetic radiation, the formula
Oh and you had to convert from eV to J then back to eV at the end.
EDIT: And
Post by: brad.j.b on November 10, 2010, 02:22:03 pm
anyone know how to solve that? :-[
you times 600eV X 1.6 X 10^-19 to get kinetic energy
then use 0.5mv^2 to get velocity
then get de broglie wavelength
which is the same as the X ray so use E=hc/wavlength
= 24,000 ev or something like that
Post by: coletrain on November 10, 2010, 02:24:26 pm
[/quote]
you times 600eV X 1.6 X 10^-19 to get kinetic energy
then use 0.5mv^2 to get velocity
then get de broglie wavelength
which is the same as the X ray so use E=hc/wavlength
= 24,000 ev or something like that
[/quote]
i did this, got like 2.4 x 10^4
Post by: 3Xamz on November 10, 2010, 02:25:52 pm
and lamda was the same as the electron? xD
Post by: Galvanic Cell on November 10, 2010, 02:26:40 pm
Post by: rubiks on November 10, 2010, 02:26:53 pm
Post by: 3Xamz on November 10, 2010, 02:28:38 pm
Phew. Nobody in my class got the same answer as me so I thought I lost 3 marks already. <3 vcenotes
We are smarter than them, so don't worry :P
Post by: 715761 on November 10, 2010, 02:29:41 pm
Post by: Xavier1234 on November 10, 2010, 02:30:08 pm
Phew. Nobody in my class got the same answer as me so I thought I lost 3 marks already. <3 vcenotes
We are smarter than them, so don't worry :P
+1! :D
Post by: gamblor0 on November 10, 2010, 02:30:18 pm
i put 24840. right you recon?
Post by: kyzoo on November 10, 2010, 02:31:45 pm
Post by: m@tty on November 10, 2010, 02:32:49 pm
Yeah I just used my original wavelength from Q7... it was a bit ambiguous, I reckon... O_O
Nah, it specifically said that the electrons are emitted with an energy of 600eV, and the question before was different.
Post by: rubiks on November 10, 2010, 02:34:53 pm
Post by: physics on November 10, 2010, 02:38:59 pm
Post by: Blakhitman on November 10, 2010, 02:52:00 pm
Post by: coletrain on November 10, 2010, 02:54:07 pm
Overall i kind of happy with this exam as physics was gonna be my 5th
Post by: Chavi on November 10, 2010, 02:59:41 pm
Post by: rubiks on November 10, 2010, 03:00:14 pm
i changed it to sceintific ie 2.4 x 10^4 should be ok right?If you did it that way shouldn't it have been 2.5x10^4?
Overall i kind of happy with this exam as physics was gonna be my 5th
Post by: simonhu81292 on November 10, 2010, 03:15:25 pm
they should accept a range because of 1.) different values of h, either 4.14x10^-15 and 6.63x10^-34 come up with slightly different answers 2.) People rounding off too earlyyeah, they usually accept the answer from certain ranges...
kyzoo, did you ace it?
Post by: 3Xamz on November 10, 2010, 03:47:38 pm
Yeah I just used my original wavelength from Q7... it was a bit ambiguous, I reckon... O_O
Nah, it specifically said that the electrons are emitted with an energy of 600eV, and the question before was different.
I used the answer from Q7) based on the fact that they have the same diffraction patterns. I stated that.
I also got ~2.4*10^5 eV, can't remember exactly but it was definitely 2.4something.
Post by: whyareyoureadingthis on November 10, 2010, 03:54:00 pm
Didn't know whether the electron speed was going to be the same or not, so I got it using KE=0.5mv^2. Was it the same or not?
Post by: schnappy on November 10, 2010, 04:12:22 pm
Post by: bblovee on November 10, 2010, 04:26:30 pm
But I don't believe vcaa is as pedantic on sig figs with physics as they are with chem
Post by: Galvanic Cell on November 10, 2010, 08:39:44 pm
Post by: Whatlol on November 10, 2010, 08:40:30 pm
If i did everything correct, but used the wrong speed (i used the stated speed from earlier), will i get any marks?
yes you should get at least 1 mark for correct working out.
Post by: 3Xamz on November 10, 2010, 09:37:32 pm
That entire a4 page is covered in writing on mine. I knew how to do it, I just kept getting different and spastic answers. I thought 24000ish would be way to high! wow I probably got the right answer but cross it off at some point :( Aw well, I'm quite confident on everything else. Not going to disappoint by looking at the 'answers'. I got concerned with the sound question, where the intensity dropped by 1/16. I couldn't evaluate the logarithm... I guess 58dB anyway. During my spare 30mins at the end I found a log button on my scientific calculator and was super happy fun times. I spent about 20 minutes of this x-ray energy question.
LOL good guess, answer was 58dB.
Post by: Greggler on November 10, 2010, 10:45:04 pm
Post by: Whatlol on November 10, 2010, 10:48:48 pm
reckon i could scrape a mark when i found both the momentum and de broglie wavelength of the x ray or whatever it was. just didnt apply it properly ><
hmm, i would like to think so since its worth 3 marks
Post by: lachymm on November 11, 2010, 01:46:56 am
Post by: Whatlol on November 11, 2010, 11:06:50 am
:( how the hell did i get 12240 eV
might of forgot the 2 when finding velocity?
Post by: Droobasaur on November 12, 2010, 06:08:08 pm
Close enough. I think I deserve full marks.
Post by: Whatlol on November 12, 2010, 06:11:52 pm
For some reason I decided to use frequency in my calculations and ended up with 26000 eV.
Close enough. I think I deserve full marks.
umm depends what frequency you found
Post by: Chavi on November 12, 2010, 06:22:02 pm
I left it as 24977 (or something like that) - instead of 2.5x10^4. Any problems>?
Post by: Whatlol on November 12, 2010, 06:23:02 pm
How many significant figures for full marks?
I left it as 24977 (or something like that) - instead of 2.5x10^4. Any problems>?
dont think it will matter to be honest. i thought physics doesnt penalise for not using significant figures?
Post by: m@tty on November 12, 2010, 07:14:59 pm
Only thing I've ever heard about significant figures in physics is that examiners get pissed if you write 587648233985462.1 instead of 5.87*10^(whatever)..
Usually 2 or 3 will suffice.