Two long and parallel straight wires A and B carrying currents of `8*0A` and `5*0A` in the same direction are separated by a distance of `4*0cm`. Estimate the force on a `10cm` section of wire A.

Explanation

Current flowing in wire `A, I_(A)=8.0A, ` Current flowing in wire B `I_(B)=5.0A`
Distance between the two wires `r=4.0cm=0.04m`
Length of a section of wire A `1=10cm=0.1m`
Force exerted on length l due to the magnetic fiedl is given as `F=(mu_(0)2I_(A)I_(B)I)/(4pir)`
where
`mu_(0)=` Permeability of free space `=4pixx10^(-7)TmA^(-1), F=(4pixx10^(-7)xx2xx8xx5xx0.1)/(4pixx0.04)=2xx10^(-5)N`
The magnitude of force is `=2xx10^(-5)N`. This is an attractive force normal to A towards B because the direction of the currents in the wires is the same.