A current-carrying wire moves toward a coil A long straight wire carrying curren
ID: 1499931 • Letter: A
Question
A current-carrying wire moves toward a coil
A long straight wire carrying current I is moving with speed v toward a small circular coil of radius r containing N turns, which is attached to a voltmeter as shown. The long wire is in the plane of the coil. (Only a small portion of the wire is shown in the diagram.)
The radius of the coil is 0.02 m, and the coil has 11 turns. At a particular instant I = 6 amperes, v = 4.4 meters per second, and the distance from the wire to the center of the coil x = 0.17 m.
up
down
left
right
into the page
out of the page
zero - no direction
(d) What is the direction of the curly electric field in the coil?
---Select---
clockwise
counter-clockwise
E = 0 in the coil
Explanation / Answer
a). Since B is inversely proportional to x, we can say that dB/B = -dx/x, or
dB/dt = -B(dx/dt)/x = -Bv/x.
B = 2mu0*I/(4pi*x) =2*4pix10^-7*6/4pi*0.17 = 7.058x10^-6 T (Ampere's law)
dB/dt = -7.058x10^-6*4.4/0.17 = -1.8269 x 10^-4 T/s.............Ans.
b). Area A = pi*0.02^2 = 1.2566x10^-3 m^2
V = N*d(BA)/dt = NA*dB/dt = 11*1.2566x10^-3*-1.8269 x 10^-4 =2.525 x 10^-6 V...........Ans.
(c) dB/dt is into the page (in the z direction).
(d) ENCis counterclockwise in the loop.