Question

Two long straight current-carrying wires run parallel to each other. The current in one of the wires is 4.8 A, their separation is 4.9 cm and they repel each other with a force per unit length of 2.0 10-4 N/m.

(a) Determine the current in the other wire.

(c) Determine what will happen if the direction of one current is reversed and tripled. (Select all that apply.)

1-The force per unit length is increased by a factor of 3.

2-The wires are repelled by each other.

3-The force per unit length is decreased by a factor of 3.

4-The wires are attracted to each other.

Answer 1

force between two parallel wires is given by F = u0i1i2L/2pid

where u0 = constnat = 4pi*10^-7 H/m,

i1, i2 are the currents ,

L s the length o the wire,

d is the distqance between these two wiresi

if current are in same directiion, there exists , they exert attractive force on each other
and if currents are in opposite direction, they exert repulsive force

so current i2 = F*(2pid)/(L* uoi1)

i2 = 2*10^-4 *2*3.14* 0.049/(4pi*10^-7 * 4.8)

i1 = 10.2 Amps

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now i2= -3i1

1-The force per unit length is increased by a factor of 3.   TRUE

2-The wires are repelled by each other.---true

3-The force per unit length is decreased by a factor of 3.-flase

4-The wires are attracted to each other.---flase