Two power lines lie parallel to each other, separated by 20 cm. They carry paral

Question

Two power lines lie parallel to each other, separated by 20 cm. They carry parallel currents, both of
magnitude 3000 A.
a) Find the force per unit length on one line due to the current in the other line. Is the force attractive or
repulsive?
b) Consider a point P lying halfway between the two lines.
- What is the magnitude of the magnetic field at P due to the two currents?
- If the currents in the two lines were antiparallel, what would be the magnitude of the magnetic field
at P?

Please help me!!!!Thank you so much

Explanation / Answer

Given that distance d = 0.20 m current I1 = I2 = 3000 A -------------------------------------------- a) The force per unit length is             F/l = (o I1I2)/(2d)                   = (4x 10^-7 T.m/A)(3000 A)^2/(2(0.20 m))                    = 1.43 N/m The force is attractive. b)     The magnitude of magnetic field at P due to the two currents is                 Bnet = 2B                          = 2(oI/(2(d/2)))                          = (2oI)/( d)                           = 2(4x 10^-7 T.m/A)(3000 A)/((0.10 m))                           = 7.639 x10^-3 T If the currents are anti parallel, so the net magnetic field at P is ZERO. If the currents are anti parallel, so the net magnetic field at P is ZERO.

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