What does $m$ mean in the De Broglie equation?

Question

The equation is: $\lambda = \frac{h}{mv}$. m here means the mass of the object while moving or while stationary?

Answer 1

The de Broglie wavelength is given by:

$$ \lambda = \frac{h}{p} $$

where $p$ is the momentum. Under non-relativistic conditions the momentum is just:

$$ p = mv $$

which gives the equation you cited. At relativistic speeds the momentum is given by:

$$ p = \gamma mv $$

where $\gamma$ is the Lorentz factor given by:

$$ \gamma = \sqrt{1 - \frac{v^2}{c^2}} $$

In these equations $m$ is the rest mass and this is an invariant and not dependent on the speed.