Physics quiz question: magnitude 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 magnitude of the magnetic force on the charge is:
(A) 0 N.
(B) 0.51 N.
(C) 0.72 N.
(D) 1.0 N.

Correct answer (highlight to unhide): (B)

The magnitude of the force of this magnetic field on this moving charge is given by:

F_B = |q·v·B·sinθ|,

where the angle θ between the charge's velocity, and the magnetic field is 45°, such that:

F_B = |(+4.0×10^–6 C)·(4.0×10⁴ m/s)·(4.50 T)·sin(45°)|,

F_B = 0.5091168825... N,

or to two significant figures, the magnitude of the magnetic force on the charge is 0.51 N.

(Response (C) is just |q·v·B|; response (D) is |q·v·B/sin(45°)|.)

Sections 30882, 30883
Exam code: quiz06Lp4s
(A) : 0 students
(B) : 24 students
(C) : 13 students
(D) : 0 students

Success level: 65%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55