When to use De Broglie equation? [ENDORSED]

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

Veeda Khan 2E
Posts: 52
Joined: Wed Sep 30, 2020 10:00 pm

When to use De Broglie equation?

Just to make sure I'm understanding this, when you have the velocity + mass but need the wavelength (or vice versa) of an object you use the the De Broglie equation, but when it's hydrogen you use c=lambda x velocity?

Brittney Nguyen 2L
Posts: 106
Joined: Wed Sep 30, 2020 9:39 pm
Been upvoted: 4 times

Re: When to use De Broglie equation?

To my understanding, you use the de Broglie equation when the particle has rest mass (i.e., electrons, neutrons, atoms, etc.). Equations like c = lambda x frequency and E = h x frequency (note that V = frequency in these equations, not velocity) are used for things like photons, which have no rest mass but do still have energy.

Anna Yakura 2F
Posts: 123
Joined: Wed Sep 30, 2020 9:46 pm

Re: When to use De Broglie equation?  [ENDORSED]

You use De Broglie when its a particle (which has a mass). You use the other equation for things like photons, which don't have a mass. Hope this helps!

MHarrold_1E
Posts: 105
Joined: Wed Sep 30, 2020 9:47 pm
Been upvoted: 2 times

Re: When to use De Broglie equation?

You can use the de Broglie equation to find wave-like properties of any object with velocity. If you have the mass and velocity of an object, you can find wavelength. You can also manipulate the equation depending on the information you are given in the problem.

sophie esherick 3H
Posts: 114
Joined: Wed Sep 30, 2020 9:35 pm
Been upvoted: 6 times

Re: When to use De Broglie equation?

Hi! You use De Broglie when its a particle or object has a rest mass that is specified. You use the other equation, c = lambda(frequency) for things like photons (EM radiation), which do not have a rest mass but have energy.

Crystal Hsueh 2L
Posts: 115
Joined: Wed Sep 30, 2020 9:35 pm
Been upvoted: 1 time

Re: When to use De Broglie equation?

Usually when the mass of the particle in the problem is given to me I go straight to De Broglie! If you are asked to find the wavelength of a photon (where you are not given a mass) you would use E = hv.

Ayesha Aslam-Mir 3C
Posts: 112
Joined: Wed Sep 30, 2020 9:43 pm

Re: When to use De Broglie equation?

On the formula sheet, we have the De Broglie equation, and another one that is E=momentum times c. In which case would we use one or the other? Or are both valid?

Brittney Nguyen 2L
Posts: 106
Joined: Wed Sep 30, 2020 9:39 pm
Been upvoted: 4 times

Re: When to use De Broglie equation?

Ayesha Aslam-Mir 2E wrote:On the formula sheet, we have the De Broglie equation, and another one that is E=momentum times c. In which case would we use one or the other? Or are both valid?

I've personally never used that equation. I just know that it's used in the derivation of the De Broglie equation!