Two wires carry current I 1 = 71 A and I 2 = 33 A in the opposite directions par

Question

Two wires carry current I1 = 71 A and I2 = 33 A in the opposite directions parallel to the x-axis at y1 = 9 cm and y2 = 15 cm. Where on the y-axis (in cm) is the magnetic field zero?

If the field is 8 mT, the mass of the particle is 22·109 kg, its initial speed 8.9 m/s, and its charge -6 C, what is the magnitude of its acceleration?Ans: 19.4 m/s^2

What is the speed of the particle 0.3 seconds later?

3. You know you should not have bought the "MRI in a Box" kit from the Home Shopping Channel. Its main solenoid is supposed to have a radius of r=0.12 m, a length of L=0.15 m, and 12000 windings. The wire they give you has a resistance of 13 m per meter. With only air inside, it's supposed to generate a field of 6.4 Tesla. What current would be needed? 63.7 A

How much power would your MRI device consume in steady operation?

An electron enters a homogeneous magnetic field pointing out of the screen. Of the indicated trajectories, which one is the most likely?
A
B
C
D
E

Explanation / Answer

1.

Note that the magnetic field due to a long wire is

B = uo I / (2 pi r)

where r is the distance from the wire, and the direction being determined by the right hand rule.

By inspection, the location of this point must be on top of I2, as it is the weaker current.

Let y = the y coordinate where the B field is 0.

Thus,

B1 = uo I1 / (2 pi (y - 0.09))

B2 = uo I2 / (2 pi (y - 0.15))

Thus, the net B field, as they are in opposite directions, is

Bnet = 0 = uo I1 / (2 pi (y - 0.09)) - uo I2 / (2 pi (y - 0.15))

Solving for y,

y = 0.2021 m or

y = 20.21 cm [ANSWER]

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