Physics quiz question: direction of magnetic force on moving charge

Physics 205B Quiz 6, spring semester 2014
Cuesta College, San Luis Obispo, CA

A q = +4.0 µC charge moves at a speed of 
4.0×10⁴ m/s through a uniform magnetic field with magnitude 4.50 T. The direction of the magnetic force on the charge is:
(A) up ↑.
(B) down ↓.
(C) left ←.
(D) right →.
(E) into the page ⊗.
(F) out of the page ⊙.
(G) (Some other (diagonal) direction not listed above.)
(H) (No direction, as the magnetic force is zero.)

Correct answer (highlight to unhide): (F)

Using the first right-hand rule (RHR1), where the thumb points along the direction of the (positive) charge's velocity v: diagonally in the plane of the page; the index finger along the direction of the magnetic field B: up along the plane of the page; the middle finger then must point perpendicularly out of the page of the page, which is the direction of the force F on this (positive) charge. (The force would be in the opposite direction given by the middle finger if the charge was instead negative.)

Sections 30882, 30883
Exam code: quiz06Lp4s
(A) : 5 students
(B) : 2 students
(C) : 2 students
(D) : 2 students
(E) : 3 students
(F) : 18 students
(G) : 5 students
(H) : 0 students

Success level: 49%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55