Quantum phsics and x-ray physics

1. May 2, 2005

is there anyone on here who could help me out with either of these?

2. May 2, 2005

heres a sample question
Calculate the de Broglie wavelength of a 5,000 kg truck traveling at 80 kph. (Round answer to nearest hundredth.)

3. May 2, 2005

StatusX

Help you with what? Are you doing a project? Or do you just have a bunch of questions? Just post your questions and people will help you with them. For the one above, that's just plug and chug. The formula for deBroglie wavelength is p = h/λ, where h is plancks constant.

4. May 2, 2005

λ=5.97x e-39
tahts the answer now how did i get it
and i have alot of questions like this i just dont know how they are done

5. May 2, 2005

ill post 2 mroe then i have to go for a while
Calculate the uncertainty of the velocity of a particle confined to a space of 10-9 m if the particle is an electron
(me = 9.1 · 10-31 kg)

delta v=__________m/sec

and

Calculate the uncertainty of the velocity of a particle confined to a space of 10-9 m if the particle is a proton
(mp = 1.7 · 10-27 kg)

delta v=___________m/sec

tahnks for your help
btw if you didnt get this already i want how to get the answer not the answer

6. May 2, 2005

StatusX

There are no concepts here. You just find p (which is m*v), look up the value for h, plug them in, and solve for λ. Feel free to ask any other questions right here, you don't need to ask for permission.

7. May 2, 2005

StatusX

Are you asking where the formula comes from? If so, that's a little complicated, but I can give you a rough sketch.

If you're asking how to plug numbers into a formula, you need to take a lot more math classes before you get into QM.

8. May 2, 2005

m and v mass and velocity
is that right? so the answer would be 5000*80*6.63e-34 correct? but it doesnt get the correct answer

and yes i know how to as you say "plug and chug"

9. May 2, 2005

StatusX

p=h/λ, so λ=h/p. Why are you doing these problems if you're still not comfortable with basic high school physics and math?

10. May 3, 2005

that still doesnt get the correct answer
λ=h/p
6.63e-34/(5000*80) =λ doesnt get the correct answer so either your wrong or you jsut dont get what im asking for can you do teh question if so past your work on this page thats all i ask for

11. May 3, 2005

O_o

Make sure everything is in SI units before you start solving.

Last edited: May 3, 2005
12. May 3, 2005

Gokul43201

Staff Emeritus
No, whiteshado : StatusX is perfectly correct.

You need to learn the following things first (way before you do Quantum Physics) :

1. Basic algebra and arithmetic
2. Units and dimensions

take care of these and you'll be able to handle the first problem.

We will not provide answers/solutions to your problems. That is not what this forum is meant for. If you need help with specific concepts, ask away, but if you have homework to do, we can not help unless you show what effort you have made.

13. May 3, 2005

no i have the answers i posted the answer
λ=5.97x e-39
but how did i get it?

14. May 3, 2005

ok how about a simpler one i need the equation for finding the frequency for a wavelength

15. May 3, 2005

dextercioby

What's the SI unit for velocity ?

Daniel.

16. May 3, 2005

juvenal

The answer you give is meaningless. You have no units (unless that x you have is not "times" but some constant with a unit). Wavelength is not dimensionless.

17. May 3, 2005

Calculate the de Broglie wavelength of a 5,000 kg truck traveling at 80 kph
λ=5.97 e-39m

18. May 3, 2005

dextercioby

Alright.Now did u find out how to derive this result...?

Daniel.

19. May 3, 2005

sigh taht is waht i am trying to find out... but no one reads on this fourm

and someone said im am just trying to get people to do my homework well how many people who want their homework done post the answer to their questions

20. May 3, 2005

dextercioby

You've been told that

$$\lambda \ \left(\mbox{m}\right)=\frac{h \ \left(\mbox{Kg}\cdot\frac{\mbox{m}}{\mbox{s}^{2}}\cdot\mbox{m}\cdot\mbox{s}\right)}{p \ \left(\mbox{Kg}\cdot\frac{\mbox{m}}{\mbox{s}}\right)}$$

Now plug the values paying attention to the units.Planck's constant is given in $\mbox{J}\cdot\mbox{s}$ which u can show to be equal to $\mbox{Kg}\cdot\frac{\mbox{m}}{\mbox{s}^{2}}\cdot\mbox{m}\cdot\mbox{s}$.

U need to find the truck's momentum in SI units.Basically,u need to convert its speed from $\frac{\mbox{Km}}{\mbox{hr}}$ to $\frac{\mbox{m}}{\mbox{s}}$.

Daniel.

Last edited: May 3, 2005