## Rest Mass

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

Brandon Mo 4K
Posts: 70
Joined: Fri Sep 28, 2018 12:15 am

### Rest Mass

Does basically anything have rest mass? During the lecture, Dr. Lavelle said that photons have no rest mass. Does that mean we can use DeBroglie's equation on anything except photons?

Aaron Ang 4H
Posts: 30
Joined: Fri Sep 28, 2018 12:28 am

### Re: Rest Mass

No not everything has rest mass. For example, you could not use De Broglie's equation to solve for the wavelength of light because it is massless. You could only use this equation for anything that has a mass.

Jessica Chen 1F
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

### Re: Rest Mass

Actually, you can use DeBroglie's equation on photons. Even though photons have no rest mass, they do have a nonzero momentum. Thus, the wavelength relationship still works for photons, you just have to use their momentum and the equation λ=h/p for photons.

Lydia Luong 4L
Posts: 59
Joined: Fri Sep 28, 2018 12:24 am

### Re: Rest Mass

No, there are things that you cannot use De Broglie's equation on because they do not have rest mass. You can only use De Broglie's equation on things that have rest mass.

WilliamNguyen_4L
Posts: 65
Joined: Fri Sep 28, 2018 12:28 am

### Re: Rest Mass

Rest mass is the mass of the object when it has no momentum. Since photons are never at 0 momentum, light is something that has no rest mass. De Broglie’s equation can be used to transition between dealing with particle properties and wave properties.

Connie Chen 3D
Posts: 31
Joined: Mon Jan 08, 2018 8:12 am

### Re: Rest Mass

A good rule of thumb is that problems with DeBroglie's equation are almost always large objects such as baseballs or cars. Those are able to be stopped (have no momentum) and therefore have a rest mass.

Manas Jinka
Posts: 32
Joined: Fri Sep 28, 2018 12:26 am

### Re: Rest Mass

You can only use the equation on objects that have a mass when their momentum is 0.