# DeBroglie wavelength, kE to (p) conversion?

1. Aug 29, 2011

### Joel DB

I have a relatively simple question. I should know this, but...
I need to solve for the deBroglie wavelength when only the kinetic energy is known. Shouldn't I be able to convert kE to momentum (p), when the object does not have a known velocity or mass...?

Much thanks...
JD

2. Aug 29, 2011

### Hootenanny

Staff Emeritus
No. You need both the rest mass and the velocity to determine the kinetic energy of a relativistic particle. Alternatively, you can use the total energy and the rest mass to determine the momentum (essentially the same thing).

However, if you know that the particle is moving at non-relativistic speeds, or very close to the speed of light, then there are some approximations you can use. But again, the usefulness of these depends on what you know.

Perhaps it would be easier if you tell use precisely what you know.

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