Question
11. Two wires, each having a weight per unit length of 1.0*10^-4 N/m, are strung parralel, one 0.10m above the other. If the wires carry the same current, though in opposite directions, how great must the current in each wire be for the magnetic field of the lower conductor to balance the weight of the upper conductor?
THE CORRECT ANSWER IS D
Neo-Flex by Ergotron F-AT). 11. Two wires, each having a weight per unit length of 1.0 x 10* Nm, are strung parallel, one 0.10 m above the e the wires carry the same current, though in opposite directions, how great must the current in each wire be for the m. field of the lower conductor to balance the weight of the upper conductor? A) 5.2 A B) 3.4 A C) 2.3 A D) 7.1 A E) 8.3 A d-O. Im -> I> Somal F; BIL *>| x16" A do L = lalo | 12. A 40-turn circular coil (radius = 4.0 cm, total resistance = 0.20 2) is placed in a uniform magnetic field dir perpendicular to the plane of the coil. The magnitude of the magnetic field varies with time as given by B = 50 sin( mt where t is measured in s. What is the magnitude of the induced current in the coil at 0.10 s? A) 50 mA B) 1.6 AT NE 10 9 0.32 A r. 4 cm D) zero E) 0.80 A R = 0.20 E-01 S B50 (10ne) Snem) Sa(7) =0 13. A long straight wire is parallel to one edge and is in the plane of a single-turn rectangular loop as shown. If th moving in the plane shown so that the distance x changes at a constant rate of 20 cm/s, what is the magnitude of th induced in the loop at the instant x= 5.0 cm? Let /= 50 A, a 50 cm, b 6.0 cm. - MOI A = xy 27 -1. Say 20 A) 11 V B) 22 JAN C) 27 AV D) 16 JAN E 34 X=5cm E--1 je da E--Bjat Ie sot au e M b = 40 Cn E--Balx b Page 4
Explanation / Answer
here,
11)
weight per unit length = 1 * 10^-4 N/m
r = 0.1 m
let the current in each wire be I
equating the forces vertically
magnetic force between the wires = weight
u0 * I^2 * L /( 2 * pi * r) = W
1.26 * 10^-6 * I^2 /( 2 * pi * 0.1) = W/L
1.26 * 10^-6 * I^2 /( 2 * pi * 0.1) = 1 * 10^-4
solving for I
I = 7.1 A
the current in each wire is 7.1 A
