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\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.

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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

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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...

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