d
Current flowing in wire \(A , I_{A}=8.0 \,A\)

Current flowing in wire \(B , I_{B}=5.0 \,A\)

Distance between the two wires, \(r=4.0 \,cm =0.04 \,m\)

Length of a section of wire A, \(l=10\, cm =0.1 \,m\)

Force exerted on length \(l\) due to the magnetic field is given as:

\(B=\frac{\mu_{0} 2 I_{A} I_{B} l}{4 \pi r}\)

Where,

\(\mu_{0}=\) Permeability of free space \(=4 \pi \times 10^{-7} \,T\,m\,A ^{-1}\)

\(B=\frac{4 \pi \times 10^{-7} \times 2 \times 8 \times 5 \times 0.1}{4 \pi \times 0.04}\)

\(=2 \times 10^{-5} \;N\)

The magnitude of force is \(2 \times 10^{-5}\,N\). This is an attractive force normal to A towards B because the direction of the currents in the wires is the same.