Electromagnetism - Lorentz Force

A negative test charge is moving near a long straight wire in which there is a current. A force will act on the test charge in a direction parallel to the direction of the current if the motion of the charge is in a direction

A. Toward the wire
B. Away from the wire
C. The same as that of the current
D. Opposite to that of the current
E. Perpendicular to both the direction of the current and the direction toward the wire

(GR8677 #29)

Solution:

Right Hand Rule #1

 

In this case, the force is parallel to the current,

 

Lorentz Force:

Right hand rule #2:

 

→ For positive charge:

→ For negative charge:

 

Therefore, the motion of the charge is in a direction toward the wire:

 

Answer: A



Alternative Solution:

 

Let the current points upwards along the page →
From the left side of the current, magnetic field is coming out of the page → 
From the right side of the current, magnetic field is going into the page → 

Lorentz Force:
Negative test charge →
If force parallel to current →
Magnetic field (on the right side) → 
Direction of ?



Using the same method, from left side: