Why does a closed current carrying coil experience no force when placed in a uniform electric field, whereas a charge moving with constant velocity through a uniform electric field does?
2 Answers
A current carrying coil experiences no net force in a uniform electric field because it is electrically neutral. For each positive charge in the coil with a force $\vec F = q \vec E$ there is a corresponding negative charge with force $-\vec F =-q \vec E$. The isolated charge is not electrically neutral.
The motion of the isolated charge is irrelevant as is the motion of the charges in the current.
Answer: a current carrying loop is Net neutral, although there are negative charges causing a current. there are also an equal amount of positive charges that aren't moving. thus there's a net zero charge on the wire.
And for a UNIFORM magnetic field, A current carrying loop will experience a net zero force aswell, however WILL experience a net TORQUE
$$\int I dl × B $$ B is independent of the integral as its uniform $$(\int I dl )×B $$
For a constant current I is also independent of the integral thus
$I (\int dl) × B$
For a closed loop $\int dl$ is zero, remember this is the VECTOR element dl
so I*0×B = 0