התאבכות- פיזור בראג

[liat2186]

התאבכות- פיזור בראג

לגבי שאלה מספר 3. אני צריכה להשתמש בנוסחאות הרגילות של התאבכות או בנוסחת בראג? מה שניסיתי לעשות- מצאתי את טטא לפי נוסחת בראג, ואז אמרתי שהרדיוס R=D*tan(teta ) aaa וזה לא נכון... למה זאת לא הדרך? תודה על העזרה!

 

[johngalt2]

Do you know what's the Bragg condition?

You simply need to use it. The energy of the electrons gives you their velocity, which gives you their momentum and thus their wavelength. Then you simply need to use the bragg condition: l = 2 d sin(theta), where l is their wavelength (you're looking for the first order scattering), and then use the formula you wrote in your question, but with 2theta of course.

 

[liat2186]

היי

תודה רבה. אני ניסיתי להשתמש באנרגיה ובנוסחה לאורך גל של דה ברולי, אבל השתמשתי בה לא נכון. הנוסחה של אורך גל דה ברולי = (קבוע פלנק כפול מהירות האור)/ (אנרגיה) מדברת על האנרגיה הכוללת של חלקיק??

 

[johngalt2]

but

you see that these are electrons, not photons. They have a rest mass, and the "formula" you wrote assumes the particle moves at the speed of light and that it's energy is given by: E = pc that *NOT* correct, of course, for electrons. Please, for your own sake, stop putting numbers in formulas you see in "dapei nuschaot" that you think might fit the question you were asked. What you should know is: a. for any nonrelativistic (and 60kev is certainly a nonrelativistic energy) particle, the energy/momentum relation is: E = p^2/2m b. The De-Broglie assumption is that momentum and wavelength have the following relation: pλ = h c. If the particle has no rest mass, the energy-momentum relation is: E = pc. That's it. From this you should be able to figure out what was wrong with what you said and how to fix it. Also note that c, the speed of light, shouldn't show up on a nonrelativstic equation for a particle with rest mass.