1. Two rigid rods are oriented parallel to each other and to the ground. The rod

Question

1.

Two rigid rods are oriented parallel to each other and to the ground. The rods carry the same current in the same direction. The length of each rod is 0.80 m, and the mass of each is 0.077 kg. One rod is held in place above the ground, while the other floats beneath it at a distance of 8.2 10-3 m. Determine the current in the rods.

2.

The drawing shows two long, straight wires that are suspended from a ceiling. The mass per unit length of each wire is 0.045 kg/m. Each of the four strings suspending the wires has a length of L = 1.4 m. When the wires carry identical currents in opposite directions, the angle between the strings holding the two wires is ? = 17

Explanation / Answer

1. as we know dat

B = uI/2pie R

Also net force acting on rod Fm = ILB = mg

mg = IL * uI/2pie R

I = sqrt (mg *2pie R/ uL)

hence

I = sqrt (0.077*9.8*2pie * 0.0082/4pie * 10^-7 * 0.8) = 196.66 A

2. The forces on wire are F , mg and tension T of strings.

From newtons second law when Fx = 0 and Fy = 0

we ve

-Tsin8.5 + F = 0------------(1)

and

Tcos8.5 -mg = 0-----------(2)

hence

tan 8.5 = F/mg

Also magnetic force exerted by wire ll be

F = uI^2 L/ 2pie d----------(3)

and

d/2 = 1.4sin8.5

hence

d = 0.413m

hence from eqaution 3 we ve

I = sqrt (mg tan 8.5 * 2 pie d/ Lu)

= sqrt (0.045*9.8 tan 8.5 * 2 pie* 0.413/1*4pie *10^-7 ) = 368.91 A

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