Scott Huges – MIT Lecture 10 (pdf)

http://web.mit.edu/sahughes/www/8.022/lec10.pdfScott Huges wrote:Suppose we now examine this situation from the point of view of the charge (the “charge frame”). From the charge’s point of view, it is sitting perfectly still. If it is sitting still, there can be no magnetic force!

Walter Lewin – MIT Lecture 11 (Youtube)

https://www.youtube.com/watch?v=X4dXXnUMHbQ&t=1537sWalter Lewin wrote:Magnetic fields can never do work on a moving charge. And the reason is the force is always perpendicular to the velocity v. And if the force is always perpendicular to the motion, you can change the direction of the motion, but you can't change the kinetic energy.

Don Lincoln – SCF Expert Notes (Forum)

http://sciencechatforum.com/viewtopic.php?f=84&t=8621Lincoln wrote:But what happens if you jump to the frame where the particle is not moving? With a velocity of zero, the magnetic force is zero.

Lincoln wrote:if you are moving along at the same speed as the current, there is no current and, consequently, you will have no magnetic force.

Lincoln wrote:Now, assume that the particle q is moving at the same velocity as the current. In this frame, q is stationary. But the current in the wire is also stationary. Thus I = 0, v = 0. and therefore F(magnetic) = 0.

1. On Lincoln's statementsThe v in Lorentz Force F = qvB is the relative velocity between the field lines B and a charged particle q. It does not matter whether the charged particle moves or the field lines move. All that matters is the relative velocity v, which is not zero in either frame. If the charged particle is at rest, the field lines B move at v relative to the particle. If the field lines B are at rest, the charged particle q moves at v relative to the field lines B.

The current in a wire is not zero if you move at the same speed as electrons. If you move at the same speed as electrons, the protons in the wire appear to move in the opposite direction. Therefore, the current is never zero when you move at the same speed as electrons. Therefore, I <> 0; we already know v <> 0; and therefore F(magnetic) <> 0.

2. On Walter Lewin's statements Magnetic field B does indeed do work on a moving charge. It's the essence of Lorentz force. A moving charge in a magnetic field experiences a force. And indeed, its kinetic energy changes upon interaction as does its direction.

3. On Scott Huges' statementsIn the particle frame, where the charged particle is sitting still, the field lines B move at v relative to the particle. Therefore, a force is experienced by the particle, given by F = qv * B.

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PS. Even the Wikipedia entry on the magnetic force term

here, asserts that v = 0, in the charged particle frame and therefore, Lorentz force (magnetic) is zero.

wikipedia wrote:A charge q in the conductor will be at rest in the conductor frame. Therefore, the magnetic force term of the Lorentz force has no effect