## De Broglie's equation and Heisenberg's equation

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

Amy Perez 2K
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Joined: Fri Sep 25, 2015 3:00 am

### De Broglie's equation and Heisenberg's equation

Given the equations, De Broglie's wave equation and Heisenberg's indeterminacy equation, how would we know which one to use and for what? Is it dependent on the fact that one is used for an object with a rest mass and the other isn't?

Andrew Yoon 1L
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Joined: Fri Sep 25, 2015 3:00 am

### Re: De Broglie's equation and Heisenberg's equation

These two equations have entirely different purposes.

The De Broglie's equation is used to find the wavelength of a particle from its momentum (or the momentum of a particle from its wavelength).

On the other hand, the Heisenberg uncertainty equation is finding the range of positions that a particle with a given momentum can be at OR the range of velocities given a position.

Basically, if we are given the momentum of a particle, we can find the wavelength using the De Broglie's equation and the range of positions that it can be at using the Heisenberg uncertainty equation.

Not sure about the rest mass portion of your question, but I think that it doesn't matter whether or not a particle has a resting mass since all we care about in these equations is the particle's momentum, which implies that the particle is moving.

Hope that this helped.

Shaye Busse 3B
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Joined: Fri Sep 25, 2015 3:00 am

### Re: De Broglie's equation and Heisenberg's equation

Additionally, when Heisenberg's equation is intended to be used to determine the approximate velocity and subsequently the approximate momentum of extremely small particles, such as electrons. This is the experiment used to find these value is uncertain in its results due to the nature of the electrons being observed.

When The electron is passed through a first beam of light, it is hit off-course in an unpredictable direction, making the final distance traveled when it passes a second beam of light unclear. Because of this, the final calculated velocity and distance can not be definite values.

Larger particles would not use Heisenberg's equation to calculate the velocity and momentum. This is because the momentum of the larger particles is so much greater than that of the photons from the light beam that their path is not disturbed, maing the distance and velocity very clearly measured.

Amy Perez 2K
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Joined: Fri Sep 25, 2015 3:00 am

### Re: De Broglie's equation and Heisenberg's equation

How do we know when to use which one, will it typically be stated in the question?

David Hong 3L
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Joined: Fri Sep 25, 2015 3:00 am

### Re: De Broglie's equation and Heisenberg's equation

It will not be directly stated, but if you know what the equations mean, then it will be easy to see which equation you need to use.
Like the posts above say, you use the de Broglie equation to find the wavelength in which planck's constant/momentum = wavelength. The Heisenberg indeterminacy equation deals with the position of a particle. Delta X is the position, which is measured in mass and delta P is momentum, which is mass x velocity. If a problem involves wavelength, then it will most likely involve using the de Broglie equation.