Consider a proton that in the unprimed frame is at rest at point $P$ midway between two positively charged thin rods parallel to the $x$ axis. The top rod moves with speed $\mid \vec{v}$ in the $+x$ direction as shown. Both rods have the same charge per unit length $\lambda$ in the unprimed frame.

for section (d) consider viewing the situation in a primed frame in which the top rod is at rest. Specify the direction of
-(c) $\vec{F}_{e m}=0$ on the proton in the unprimed frame.

Question

Consider a proton that in the unprimed frame is at rest at point $P$ midway between two positively charged thin rods parallel to the $x$ axis. The top rod moves with speed $\mid \vec{v}$ in the $+x$ direction as shown. Both rods have the same charge per unit length $\lambda$ in the unprimed frame.
  
for section (d) consider viewing the situation in a primed frame in which the top rod is at rest. Specify the direction of
-(c) $\vec{F}_{e m}=0$ on the proton in the unprimed frame.

Quizplus · Accepted Answer

The electric field is zero in the unprimed frame because the proton is moving with a constant velocity.

Consider a Proton That in the Unprimed Frame Is at Rest