# Homework Help: X-ray Wavelengths

1. Jul 25, 2008

### conniechiwa

1. The problem statement, all variables and given/known data
The tube in a medical research X-ray unit uses lead (Z=82) as it's target. Assume the electrons are accelerated through the voltage calculated in part (b). What is the wavelength of the Kα line?

2. Relevant equations
KE=-13.6 ev ((Z-1)squared) / (1squared)
KE=PE=VQ
E=QV
λ=hc/E

3. The attempt at a solution
KE=-13.6 ev ((Z-1)squared) / (1squared)
KE =-13.6 ev ((82-1)squared)/ 1 squared)
KE=89229.6 ev

KE=PE=QV
89229.6=(1.602E-19 J/ev)V
V=89229.6 V

E=QV
E=(1.602E-19 C)(89229.6V)
E=1.429E-14 J

λ=hc/E
λ=((6.63E-34 J*s)(3E8 m/s))/(1.429E-14 J)
λ=1.3856E-11 m = 0.013856 nm

I'm not sure what's wrong... I correctly solved for KE and V, but I can't seem to solve for λ.

2. Jul 25, 2008

### Astronuc

Staff Emeritus
I'm not sure where part b is, but think about the energies.

The accelerated electron must have enough energy to dislodge a K-electron from the lead atom.

Then another orbital electron will fall from a higher state to the spot in the K-shell, so the X-ray energy represents a difference in energy levels of atomic electrons. What's the significance of Kα?

3. Jul 26, 2008

### conniechiwa

Oh okay I got it now. Thanks!