1) A 2.8 m long straight horizontal wire carrying a current of 4.9 A along the +

Question

1) A 2.8 m long straight horizontal wire carrying a current of 4.9 A along the +x-direction is in a region of uniform magnetic field, B. If the mass of this wire is 0.4 kg, find the magnitude and direction of the magnetic field necessary to have this wire "float" in the Earth's gravitational field. (Assume the force due to gravity is in the ?y-direction.)

2) Calculate the magnetic field strength a distance of 0.22 m along the +y-axis from a long straight wire carrying a current of3.1 A to the right along the +x-axis.

3) Calculate the magnitude of the magnetic field from a circular loop of wire of radius 0.23 m, carrying a current of 2.2 A, and with 250 turns of wire at a distance of 1.3 m away from the loop along the axis of the loop.

Explanation / Answer

1)
FB = Fg

B*I*L*sin(90) = mg

B = m*g/(I*L)

= 0.4*9.8/(4.9*2.8)

= 0.286 T

direction of B should be towards -z axis


2)

B = mue*I/(2*pi*r)

= 4*pi*10^-7*3.1/(2*pi*0.22)

= 2.818*10^-6 T

3)


B = N*mue*I*R^2/2*(R^2+x^2)^(3/2)

B = 250*4*pi*10^-7*2.2*0.23^2/2*(0.23^2+1.3^2)^1.5

= 7.94*10^-6 T

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