Is the Total Momentum in QED Actually Total Angular Momentum?

In summary, the conversation discusses a text on QED that equates the vector potential to electrodynamic momentum using the de Broglie relationship. The current flow in a conductor is predicted by considering the total momentum of the charge in relation to the electrodynamic. However, when looking at the dimensions, it is found that the electrodynamic part has the units of angular momentum while the total momentum is assumed to be linear momentum. The validity of this assumption is questioned and it is suggested that the total momentum being considered in the text may actually be the total angular momentum. The need for proper referencing and clarification is emphasized.
  • #1
AJ Bentley
668
0
I was just reading a text on QED that equates the vector potential to electrodynamic momentum using the de Broglie relationship.
At a later stage, the current flow in a conductor is predicted by considering the total momentum of the charge in relation to the electrodynamic.
Everything works out and it all fits.

But when I look at the dimensions, I find that the electrodynamic part has the units of angular momentum. Whereas the total momentum is of course, well, I assume it's momentum.

Is this valid? can I simply add angular and linear momentum and equate that total to wavenumber.

Or is it that the total momentum being considered in the text is in actual fact the total angular momentum? Presumably the author felt it too obvious to mention?
 
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  • #2
AJ Bentley said:
I was just reading a text on QED that equates the vector potential to electrodynamic momentum using the de Broglie relationship.

reference please.

But when I look at the dimensions, I find that the electrodynamic part has the units of angular momentum. Whereas the total momentum is of course, well, I assume it's momentum.

Is this valid?

reference please.

Or is it that the total momentum being considered in the text is in actual fact the total angular momentum? Presumably the author felt it too obvious to mention?

Reference please.

How can anyone have a clue how to answer you correctly, AJ, if you haven't given the derivation OR the reference??

...
 
  • #3
Many texts refer to angular momentum simply as 'momentum'.
 
  • #4
Thank you, that's what I thought.
(The actual context of the question isn't important Creator - there's no point anyone delving into the text)
 
Last edited:

1. What is the difference between momentum and angular momentum?

Momentum is a measure of an object's motion, taking into account its mass and velocity. It is a vector quantity, meaning it has both magnitude and direction. Angular momentum, on the other hand, is a measure of an object's rotational motion. It takes into account the object's mass, velocity, and distance from a fixed axis of rotation. It is also a vector quantity.

2. How is momentum related to angular momentum?

Momentum and angular momentum are related in that they both involve the concept of motion. Momentum is the linear motion of an object, while angular momentum is the rotational motion of an object. They are both conserved quantities, meaning they cannot be created or destroyed, only transferred or converted.

3. How do you calculate momentum and angular momentum?

Momentum is calculated by multiplying an object's mass by its velocity. Mathematically, it can be expressed as p = mv, where p is momentum, m is mass, and v is velocity. Angular momentum is calculated by multiplying an object's moment of inertia by its angular velocity. It can be expressed as L = Iω, where L is angular momentum, I is moment of inertia, and ω is angular velocity.

4. What are some real-life examples of momentum and angular momentum?

Examples of momentum in everyday life include a car moving down a road, a ball being thrown, or a person running. Examples of angular momentum include a spinning top, a rotating planet, and a swinging pendulum.

5. How do changes in momentum and angular momentum affect an object?

Changes in momentum and angular momentum can affect an object's motion. An object with a larger momentum will be more difficult to stop or change direction compared to an object with a smaller momentum. Similarly, an object with a larger angular momentum will be more difficult to stop or change its rotation compared to an object with a smaller angular momentum.

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