GREPhysics.NET
GR | # Login | Register
   
  GR9277 #80
Problem
GREPhysics.NET Official Solution    Alternate Solutions
\prob{80}
A beam of electrons is accelerated through a potential difference of 25kV
in an x-ray tube. The continuous x-ray spectrum emitted by the target of the tube will have a short wavelength limit of most nearly

  1. 0.1 angstroms
  2. 0.5 angstroms
  3. 2 angstroms
  4. 25 angstroms
  5. 50 angstroms

Quantum Mechanics}Planck Energy

The key equation is E=hc/\lambda. Since hc=1.24E-6eVm and E=25E3eV=2.5E4eV, one can immediately plug the quantities in to solve for \lambda=hc/E = 1.24E-6/2.5E4=0.5E-10, which is just choice (B).

No knowledge of X-rays required, other than the elementary knowledge that it's a electromagnetic wave and allows one to write the Planck energy as E=hf = h c/\lambda.

See below for user comments and alternate solutions! See below for user comments and alternate solutions!
Alternate Solutions
There are no Alternate Solutions for this problem. Be the first to post one!
Comments
omidkhakpour
2014-02-03 08:59:51
this quastion is wrong becaus the 25KV is "25K electron volt". The question said it's V = volt, not eV=electron volt
omidkhakpour
2014-02-03 09:54:59
yo think this wrong but q = e, so we get straight back to electron volts.
NEC
omidkhakpour
2014-02-03 08:59:34
this quastion is wrong becaus the 25KV is "25K electron volt". The question said it's V = volt, not eV=electron voltNEC
ali8
2011-07-13 08:28:32
Sorry but, how did all of you assumed that the 25KV is "25K electron volt". The question said it's V = volt, not eV=electron volt.

So we should use E=qV...

itorsics
2011-09-11 00:29:31
And q = e, so we get straight back to electron volts...
Answered Question!
gumby
2009-10-29 21:43:39
Memorize this useful quantity! It's faster than trying to multiply h*c all the time.
h c = 1239.87  eV nm
Mnemonic: first 3 digits, last 3 digits.
nyuko
2009-10-30 21:59:16
I think memorizing hc=1240eVnm is good enough
apr2010
2010-04-08 09:15:47
On the order of atom lattice constants / near neighbor distances (\approx  1 \AA ), so it should be 0.5 or smaller. The resolution is in general not as good with x-ray tubes, that's why I have chosen B.
gravity
2010-11-09 05:12:06
I think memorizing hc = 5/4 KeV nm is good enough
neon37
2010-11-12 06:21:21
try 1000 eVnm even easier.
NEC

Post A Comment!
Username:
Password:
Click here to register.
This comment is best classified as a: (mouseover)
 
Mouseover the respective type above for an explanation of each type.

Bare Basic LaTeX Rosetta Stone

LaTeX syntax supported through dollar sign wrappers $, ex., $\alpha^2_0$ produces .
type this... to get...
$\int_0^\infty$
$\partial$
$\Rightarrow$
$\ddot{x},\dot{x}$
$\sqrt{z}$
$\langle my \rangle$
$\left( abacadabra \right)_{me}$
$\vec{E}$
$\frac{a}{b}$
 
The Sidebar Chatbox...
Scroll to see it, or resize your browser to ignore it...