Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 19.65
Consider a long straight wire that carries a current of 1.5 A. What is the magnitude of the magnetic field at the location shown, 0.20 m below the wire? (A) 1.5e-6 T.
(B) 4.7e-6 T.
(C) 9.4e-6 T.
(D) 1.9e-5 T.
Correct answer: (A)
The magnitude of the magnetic field of a wire with current I is given by:
B = mu_0*I/(2*pi*r),
where mu_0 = 4*pi*10^7 T*m/A is the vacuum permeability, and r is the distance from the center of the wire, such that:
B = (4*pi*10^7 T*m/A)*(1.5 A)/(2*pi*(0.20 m)) = 1.5e-6 T.
Response (B) is mu_0*I/(2*r); response (C) is mu_0*I/r; response (D) is 2*mu_0*I/r.
Student responses
Section 31988
(A) : 12 students
(B) : 0 students
(C) : 0 students
(D) : 1 student
Success level: 92%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20
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