# Homework Help: An electron traveling at a speed of

1. Aug 1, 2010

### atoreta88

1. The problem statement, all variables and given/known data
An electron traveling at a speed of 6.0 x10^7 m/s. strikes the target of an x-ray tube. Upon impact, the electron decelerates to 1/4th of its original speed, emitting an x-ray in the process. What is the wavelength of the x-ray photon?

2. Relevant equations
I think I'm suppose to use the formula E=hf (eqn 1) and v=lambda*f (eqn 2)

3. The attempt at a solution
I manipulated both equations (eqn 1 and eqn 2) to get the formula E=(h*v)/(lambda), but that leaves me with two unknowns..when all I want is lambda to be the only unknown. I'm not sure how I would find the energy...and I'm not sure if I'm even using the correct formulas. Hopefully I'm on the right track???

2. Aug 1, 2010

### graphene

What you want is the wavelength of the X-ray - an EM wave. What is its speed ?

3. Aug 2, 2010

### praveenpp

we can find the wavelength of the emitted x-ray photon. using

first find the kinetic energy of the electron using K.E = 1/2 m*v^2.
then apply the formula

lambda = (h*v)/K.E

it will give the answer for you.

4. Aug 2, 2010

### Staff: Mentor

That is incorrect. Even a dimensional analysis shows that there is something wrong with that equation.

And please do not do the original poster's (OP's) work for them -- they are required to do the work themselves. You may provide hints and ask questions, in order to help them figure out the problem on their own.