### Question: How should I decide if I use DeBroglie Equation or the equation for Kinetic Energy?

Posted:

**Sun Oct 09, 2016 8:51 am**Question #33 in the book says: The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. What is the wavelenght of the ejected electron?

When I started solving the problem, the first equation that came to my mind was the kinetic energy one (as the electron was ejected and this is moving), so I applied the formula . However when comparing to the solutions, I noticed they used the DeBroglie Equation . The results were very different. How do I know when to use each of the equations?

Thanks for answering!

When I started solving the problem, the first equation that came to my mind was the kinetic energy one (as the electron was ejected and this is moving), so I applied the formula . However when comparing to the solutions, I noticed they used the DeBroglie Equation . The results were very different. How do I know when to use each of the equations?

Thanks for answering!