Two parallel, infinitely straight lines currents, I1 and I2, (but opposite in direction) are separated by a distance d. Find the magnitude of the force per length between them (“force per length” so that it wouldn’t be an infinite force between them). Indicate whether the force would be attractive or repulsive.

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Two parallel wires, separated by a perpendicular distance of 5.0 cm, carry currents of 5.0 A and 2.0 A in the same direction. What force does the 5.0-A wire exert on a 50 cm-length of the 2.0-A wire?   a. 60 μN, repulsive   b. 40 μN, attractive   c. 20 μN, attractive   d. 80 μN, attractive   e. 100 μN, attractive

Consider a long, horizontal Large Wire with current of 10 A running through it. We want to levitate a horizontal, thin, 0.50 m length of wire above it. If the thin wire has a mass of 10 grams, and a current of 300 mA, how far above the Large Wire will it hover (net force of zero) due to magnetic and gravitational forces? A. If the thin wire hovers above the Large Wire due to their magnetic fields, are their currents going the same direction, or opposite directions. Explain. B. Draw a diagram and label the directions of currents, and all other relevant quantities and vectors. C. Find the distance above the Large Wire the small thin wire will hover (net force of zero). D. Would your answers to parts A and C change if we wanted to find a distance below (rather than above) the Large Wire that the smaller thin wire could hover, due to their magnetic fields. Explain. Don't calculate any values but draw a new diagram and explain how this situation compares to the problem above.